From jscott@planetinternet.be Tue Sep 3 08:22:20 2002 From: jscott@planetinternet.be (Scott J.) Date: Tue, 3 Sep 2002 09:22:20 +0200 Subject: mutable records Message-ID: <001a01c2531a$a4c5b270$2097fea9@janxp> This is a multi-part message in MIME format. ------=_NextPart_000_0017_01C2532B.6781BC90 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Hi, Is it possible to define oject types in Haskell and what does one = propose to do it? Is it possible to define parts of a record with the help of the ST s = monad mutable during the whole program? (As is possible in Ocamel)? Thx Scott ------=_NextPart_000_0017_01C2532B.6781BC90 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

Hi,

Is it possible to define = oject=20 types in Haskell and what does one propose to do = it?

Is it possible to define parts of a = record =20 with the help of the ST s monad = mutable during=20 the whole program? (As is possible in Ocamel)?

Thx

Scott

------=_NextPart_000_0017_01C2532B.6781BC90-- From chak@cse.unsw.edu.au Tue Sep 3 09:37:18 2002 From: chak@cse.unsw.edu.au (Manuel M T Chakravarty) Date: Tue, 03 Sep 2002 18:37:18 +1000 (EST) Subject: mutable records In-Reply-To: <001a01c2531a$a4c5b270$2097fea9@janxp> References: <001a01c2531a$a4c5b270$2097fea9@janxp> Message-ID: <20020903.183718.295402125.chak@cse.unsw.edu.au> "Scott J." wrote, > Is it possible to define oject types in Haskell and what does one propose to do it? Depends on what you mean by object types. You can surely define a record with funcions dubbing as methods and non-functional values dubbing as object data. > Is it possible to define parts of a record with the help of the ST s monad mutable during the whole program? (As is possible in Ocamel)? Just make the fields that you want to update be values of `STRef s a'. (You can also do the same with the IO monad and `IORef's.) Having said this, there are not that many situations where you need to do this (and in consequence ST-monadify your program). Purely functional updates (using the record syntax) where the system effectively copies the whole record (not all data in it, just the references to that data) is perfectly suitable in most cases. If you are concerned about efficiency first profile the code to see whether the performance bottleneck is really where you think it is. Cheers, Manuel From Chris.Angus@Lawson.com Tue Sep 3 14:06:54 2002 From: Chris.Angus@Lawson.com (Chris.Angus@Lawson.com) Date: Tue, 3 Sep 2002 14:06:54 +0100 Subject: (no subject) Message-ID: This is a multipart message in MIME format. --=_alternative 004807BB80256C29_= Content-Type: text/plain; charset="us-ascii" Does anyone know what happened to the wiki on haskell.org? There was lots of stuff there last year (mostly to do with design patterns) which seems to have been lost. Some of the links are still there but they don't go anywhere. Cheers Chris --=_alternative 004807BB80256C29_= Content-Type: text/html; charset="us-ascii"
Does anyone know what happened to the wiki on haskell.org?

There was lots of stuff there last year (mostly to do with design patterns) which seems to have been lost.
Some of the links are still there but they don't go anywhere.

Cheers

Chris --=_alternative 004807BB80256C29_=-- From jcp@ragged.cs.yale.edu Tue Sep 3 14:13:56 2002 From: jcp@ragged.cs.yale.edu (John C. Peterson) Date: Tue, 3 Sep 2002 09:13:56 -0400 Subject: Wiki problems In-Reply-To: (Chris.Angus@Lawson.com) References: Message-ID: <200209031313.g83DDug16586@ragged.cs.yale.edu> We're aware of the wiki problems. We've got out "wiki guy" working on it and I hope everything will be working again soon. We won't lose anything that's been posted to the wiki. Please be patient! John From diatchki@cse.ogi.edu Tue Sep 3 18:00:13 2002 From: diatchki@cse.ogi.edu (Iavor S. Diatchki) Date: Tue, 03 Sep 2002 10:00:13 -0700 Subject: mutable records References: <001a01c2531a$a4c5b270$2097fea9@janxp> <20020903.183718.295402125.chak@cse.unsw.edu.au> Message-ID: <3D74EA9D.4030500@cse.ogi.edu> hi, Manuel M T Chakravarty wrote: > ... > Having said this, there are not that many situations where > you need to do this (and in consequence ST-monadify your > program). Purely functional updates (using the record > syntax) where the system effectively copies the whole record > (not all data in it, just the references to that data) is > perfectly suitable in most cases. If you are concerned > about efficiency first profile the code to see whether the > performance bottleneck is really where you think it is. one situation in which i find mutable fields easier to use rather than pure updates is if the record is deep into another data structure (e.g. a list of records). modifying a record than becomes a hassle as one has to remove it from the list, create the new record, and then insert it in the list. this is particularly inconvinient if the order of the records in the list actually matters. bye iavor -- ================================================== | Iavor S. Diatchki, Ph.D. student | | Department of Computer Science and Engineering | | School of OGI at OHSU | | http://www.cse.ogi.edu/~diatchki | ================================================== From jscott@planetinternet.be Tue Sep 3 18:55:22 2002 From: jscott@planetinternet.be (Scott J.) Date: Tue, 3 Sep 2002 19:55:22 +0200 Subject: mutable records References: <001a01c2531a$a4c5b270$2097fea9@janxp> <20020903.183718.295402125.chak@cse.unsw.edu.au> Message-ID: <001601c25373$13ec8f90$2097fea9@janxp> Sorry for my late reply, But is it possible to be more specific (little examples) In Haskell one can use existential lists but I doubt about the efficiency. It is not my aim to make of everything an object like in Jave e.g. . The objects I have in mind are showable ojects: windows, scrollbars, messageboxes, etc. . Of such objects I demand fast response with respect to key input or mouse clicks. I am sure Ocamel can do that. Regards Scott ----- Original Message ----- From: "Manuel M T Chakravarty" To: Cc: Sent: Tuesday, September 03, 2002 10:37 AM Subject: Re: mutable records > "Scott J." wrote, > > > Is it possible to define oject types in Haskell and what does one propose to do it? > > Depends on what you mean by object types. You can surely > define a record with funcions dubbing as methods and > non-functional values dubbing as object data. > > > Is it possible to define parts of a record with the help of the ST s monad mutable during the whole program? (As is possible in Ocamel)? > > Just make the fields that you want to update be values of > `STRef s a'. (You can also do the same with the IO monad > and `IORef's.) > > Having said this, there are not that many situations where > you need to do this (and in consequence ST-monadify your > program). Purely functional updates (using the record > syntax) where the system effectively copies the whole record > (not all data in it, just the references to that data) is > perfectly suitable in most cases. If you are concerned > about efficiency first profile the code to see whether the > performance bottleneck is really where you think it is. > > Cheers, > Manuel > From alastair@reid-consulting-uk.ltd.uk Tue Sep 3 19:44:42 2002 From: alastair@reid-consulting-uk.ltd.uk (Alastair Reid) Date: 03 Sep 2002 19:44:42 +0100 Subject: mutable records In-Reply-To: <001601c25373$13ec8f90$2097fea9@janxp> References: <001a01c2531a$a4c5b270$2097fea9@janxp> <20020903.183718.295402125.chak@cse.unsw.edu.au> <001601c25373$13ec8f90$2097fea9@janxp> Message-ID: > In Haskell one can use existential lists but I doubt about the > efficiency. Existential lists don't have any special time overhead. All you're doing is making the typechecker happy about what you're doing. Of course, there's a small overhead in that any function you invoke on that object will almost certainly be an indirect function call rather than a direct function call so you get the same (small) overhead as in C++ virtual function calls, Haskell method calls (when not optimized away), etc. > It is not my aim to make of everything an object like in Jave > e.g. . The objects I have in mind are showable ojects: windows, > scrollbars, messageboxes, etc. . Of such objects I demand fast > response with respect to key input or mouse clicks. I am sure Ocamel > can do that. We're sure Haskell can too. You can probably translate your OCaml code fairly directly into Haskell but directly translating code which uses mutable state tends to result in unidiomatic Haskell code. If you want nice Haskell code (i.e., which exploits Haskell's strengths, plays well with other libraries, etc.) it's often best to think about the problem you're trying to solve and find a way to express that in Haskell instead of trying to express the standard solution in Haskell. For example, C/C++/Java GUIs are usually implemented by creating a bunch of objects and then connecting the objects together by invoking methods on them to add event handlers, etc. Such programs almost never change the object interconnections after this initialization phase. In effect, we have a bunch of single-assignment variables: they get initialized but never change after that. Haskell has single-assignment variables too (i.e., the normal, non-mutable variables you learn about on page 2 of any Haskell textbook) and you can often use them to express the connections between the objects. Doing this has an enormous benefit that you don't get in C, C++, Java, etc. which is that Haskell's typechecker can catch some of the errors you might make when making these object interconnections. This example probably doesn't apply to your code but it's an example of how you can eliminate gratuitious use of mutable variables from your code. The key is to ask us about the problem you're trying to solve not ask how to express the standard (imperative) solution in Haskell. -- Alastair Reid alastair@reid-consulting-uk.ltd.uk Reid Consulting (UK) Limited http://www.reid-consulting-uk.ltd.uk/alastair/ From jscott@planetinternet.be Thu Sep 5 13:24:09 2002 From: jscott@planetinternet.be (Scott J.) Date: Thu, 5 Sep 2002 14:24:09 +0200 Subject: mutable records References: <001a01c2531a$a4c5b270$2097fea9@janxp> <20020903.183718.295402125.chak@cse.unsw.edu.au> <001601c25373$13ec8f90$2097fea9@janxp> Message-ID: <001801c254d7$22ef86e0$0100a8c0@janxp> Hi, You gave me a lot of thinking about . Sill I want to make objects packed with their objects and functions. Doesn't mean that I have to use existential data types? Scott ----- Original Message ----- From: "Alastair Reid" To: "Scott J." Cc: ; Sent: Tuesday, September 03, 2002 8:44 PM Subject: Re: mutable records > > > In Haskell one can use existential lists but I doubt about the > > efficiency. > > Existential lists don't have any special time overhead. All you're > doing is making the typechecker happy about what you're doing. > > Of course, there's a small overhead in that any function you invoke on > that object will almost certainly be an indirect function call rather > than a direct function call so you get the same (small) overhead as in > C++ virtual function calls, Haskell method calls (when not optimized > away), etc. > > > It is not my aim to make of everything an object like in Jave > > e.g. . The objects I have in mind are showable ojects: windows, > > scrollbars, messageboxes, etc. . Of such objects I demand fast > > response with respect to key input or mouse clicks. I am sure Ocamel > > can do that. > > We're sure Haskell can too. > > You can probably translate your OCaml code fairly directly into > Haskell but directly translating code which uses mutable state tends > to result in unidiomatic Haskell code. If you want nice Haskell code > (i.e., which exploits Haskell's strengths, plays well with other > libraries, etc.) it's often best to think about the problem you're > trying to solve and find a way to express that in Haskell instead of > trying to express the standard solution in Haskell. > > For example, C/C++/Java GUIs are usually implemented by creating a > bunch of objects and then connecting the objects together by invoking > methods on them to add event handlers, etc. Such programs almost > never change the object interconnections after this initialization > phase. In effect, we have a bunch of single-assignment variables: > they get initialized but never change after that. > > Haskell has single-assignment variables too (i.e., the normal, > non-mutable variables you learn about on page 2 of any Haskell > textbook) and you can often use them to express the connections > between the objects. Doing this has an enormous benefit that you > don't get in C, C++, Java, etc. which is that Haskell's typechecker > can catch some of the errors you might make when making these > object interconnections. > > This example probably doesn't apply to your code but it's an example > of how you can eliminate gratuitious use of mutable variables from > your code. The key is to ask us about the problem you're trying to > solve not ask how to express the standard (imperative) solution in > Haskell. > > > -- > Alastair Reid alastair@reid-consulting-uk.ltd.uk > Reid Consulting (UK) Limited http://www.reid-consulting-uk.ltd.uk/alastair/ > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > From alastair@reid-consulting-uk.ltd.uk Thu Sep 5 13:58:09 2002 From: alastair@reid-consulting-uk.ltd.uk (Alastair Reid) Date: 05 Sep 2002 13:58:09 +0100 Subject: mutable records In-Reply-To: <001801c254d7$22ef86e0$0100a8c0@janxp> References: <001a01c2531a$a4c5b270$2097fea9@janxp> <20020903.183718.295402125.chak@cse.unsw.edu.au> <001601c25373$13ec8f90$2097fea9@janxp> <001801c254d7$22ef86e0$0100a8c0@janxp> Message-ID: > Sill I want to make objects packed with their objects and > functions. Doesn't mean that I have to use existential data types? Only if you need to hide the type of the object. If you don't need to hide the type then Haskell's typeclasses give you (what I understand of) what you want. I can write polymorphic functions which take an arbitrary type of object and invoke methods like ==, + and show (say) on it. foo :: (Eq a, Num a) => a -> String foo x = if x == 0 then "" else show (x+1) Actually, I suspect this is not quite what you want but the word 'object' has been used by so many people to mean so many things that it's only by throwing out strawmen like Haskell's typeclasses that we can understand what you actually do mean. -- Alastair Reid alastair@reid-consulting-uk.ltd.uk Reid Consulting (UK) Limited http://www.reid-consulting-uk.ltd.uk/alastair/ From Shawn@Garbett.org Thu Sep 5 09:40:09 2002 From: Shawn@Garbett.org (Shawn P. Garbett) Date: Thu, 5 Sep 2002 08:40:09 +0000 Subject: mutable records In-Reply-To: References: <001a01c2531a$a4c5b270$2097fea9@janxp> <001801c254d7$22ef86e0$0100a8c0@janxp> Message-ID: <200209050840.09665.Shawn@Garbett.org> "Object" in common parlance is an amalgam of: data structure, methods for= that=20 structure, state-boxes, and compositions of this amalgam. All developed o= ver=20 time using the age old method of accretion. It says something when Scott Meyer can make a living writing books about = what=20 you shouldn't do in C++. There's also a fellow who's put together an=20 interesting piece of criticism of OO:=20 http://www.geocities.com/tablizer/oopbad.htm. Shawn On Thursday 05 September 2002 12:58 pm, Alastair Reid wrote: > > Sill I want to make objects packed with their objects and > > functions. Doesn't mean that I have to use existential data types? > > Only if you need to hide the type of the object. > > If you don't need to hide the type then Haskell's typeclasses > give you (what I understand of) what you want. > > I can write polymorphic functions which take an arbitrary type of objec= t > and invoke methods like =3D=3D, + and show (say) on it. > > foo :: (Eq a, Num a) =3D> a -> String > foo x =3D if x =3D=3D 0 then "" else show (x+1) > > > Actually, I suspect this is not quite what you want but the word > 'object' has been used by so many people to mean so many things that > it's only by throwing out strawmen like Haskell's typeclasses that we > can understand what you actually do mean. From Tom.Pledger@peace.com Thu Sep 5 21:26:48 2002 From: Tom.Pledger@peace.com (Tom Pledger) Date: Fri, 6 Sep 2002 08:26:48 +1200 Subject: mutable records In-Reply-To: <001801c254d7$22ef86e0$0100a8c0@janxp> References: <001a01c2531a$a4c5b270$2097fea9@janxp> <20020903.183718.295402125.chak@cse.unsw.edu.au> <001601c25373$13ec8f90$2097fea9@janxp> <001801c254d7$22ef86e0$0100a8c0@janxp> Message-ID: <15735.48648.425221.379405@waytogo.peace.co.nz> Scott J. writes: : | Sill I want to make objects packed with their objects and | functions. Doesn't mean that I have to use existential data types? Sometimes you can avoid using existentials by making all your object-updating functions return the post-update object explicitly. For example: module FiniteMap where data FM k v = FM {set :: k -> v -> FM k v, get :: k -> Maybe v, toList :: [(k, v)]} module RedBlack(empty) where import FiniteMap empty :: Ord k => FM k v -- a finite map implemented as a red/black tree ... In this case, the red/black tree itself is effectively a private field of the object. The privacy is achieved by *not* making the tree a field of the FM record. Instead, it gets passed around as the parameter of an auxiliary function: -- module RedBlack, continued empty = fm emptyRedBlackMap fm rb = FM {set = \k v -> fm (extendRedBlackMap rb k v), get = \k -> ..., toList = redBlackMapToList rb} HTH, Tom From rende@cs.orst.edu Fri Sep 6 04:59:27 2002 From: rende@cs.orst.edu (Deling Ren) Date: Thu, 5 Sep 2002 20:59:27 -0700 (PDT) Subject: A problem with haskell-mode Message-ID: Hi, all, I installed the latest version of Haskell mode for emacs. Whenever I load haskell major mode by opening a haskell file, Xemacs gives me the following error message: (1) (error/warning) Error in `post-command-hook' (setting hook to nil): (void-variable imenu--index-alist) My Xemacs version is 21.4.8. It works well under GNU emacs though. Anybody has an idea how to get around it? Thanks. Deling From jadrian@mat.uc.pt Fri Sep 6 11:50:04 2002 From: jadrian@mat.uc.pt (Jorge Adriano) Date: Fri, 6 Sep 2002 11:50:04 +0100 Subject: A problem with haskell-mode In-Reply-To: References: Message-ID: <200209061150.04010.jadrian@mat.uc.pt> > Hi, all, I installed the latest version of Haskell mode for emacs. > Whenever I load haskell major mode by opening a haskell file, Xemacs gi= ves > me the following error message: > > (1) (error/warning) Error in `post-command-hook' (setting hook to nil): > (void-variable imenu--index-alist) > > My Xemacs version is 21.4.8. It works well under GNU emacs though. Anyb= ody > has an idea how to get around it? Thanks. > > Deling I had the same problem, and I found a fix somewhere.=20 Don't reember what exactly I had to change so I'll just send you my Haske= ll=20 section of xemacs init.el. By the way I get an error whenever I type "undefined". Anyone else notice= d it? (1) (error/warning) Error in `post-command-hook' (setting hook to nil):=20 (wrong-type-argument listp a ) J.A. -------------------------------------------------------------------------= ------ (setq load-path (cons "/usr/share/emacs/site-lisp/haskell-mode-1.41"=20 load-path)) (setq auto-mode-alist (append auto-mode-alist '(("\\.[hg]s$" . haskell-mode) ("\\.hi$" . haskell-mode) ("\\.l[hg]s$" . literate-haskell-mode)))) (autoload 'haskell-mode "haskell-mode" "Major mode for editing Haskell scripts." t) (autoload 'literate-haskell-mode "haskell-mode" "Major mode for editing literate Haskell scripts." t) ;(add-hook 'haskell-mode-hook 'turn-on-haskell-ghc) (add-hook 'haskell-mode-hook 'turn-on-haskell-font-lock) (add-hook 'haskell-mode-hook 'turn-on-haskell-decl-scan) (require 'imenu) (add-hook 'haskell-mode-hook 'turn-on-haskell-doc-mode) (add-hook 'haskell-mode-hook 'turn-on-haskell-indent) ;(add-hook 'haskell-mode-hook 'turn-on-haskell-simple-indent) ;(add-hook 'haskell-mode-hook 'turn-on-haskell-hugs) From simonmar@microsoft.com Mon Sep 9 14:43:26 2002 From: simonmar@microsoft.com (Simon Marlow) Date: Mon, 9 Sep 2002 14:43:26 +0100 Subject: A problem with haskell-mode Message-ID: <9584A4A864BD8548932F2F88EB30D1C60A41218D@TVP-MSG-01.europe.corp.microsoft.com> > I had the same problem, and I found a fix somewhere.=20 > Don't reember what exactly I had to change so I'll just send=20 > you my Haskell section of xemacs init.el. >=20 > By the way I get an error whenever I type "undefined". Anyone=20 > else noticed it? > (1) (error/warning) Error in `post-command-hook' (setting=20 > hook to nil):=20 > (wrong-type-argument listp a ) I'm officially the maintainer of the emacs Haskell mode since Reuben Thomas left, but I deleted the section of my brain that contained my knowledge of emacs lisp in order to make more room for GHC, so I'm not a very effective maintainer I'm afraid :( Offers to take over the maintainership are entirely welcome, but in the meantime I'm happy to add any fixes for these kinds of problems to the web page and/or the source. Cheers, Simon From diatchki@cse.ogi.edu Mon Sep 9 21:45:37 2002 From: diatchki@cse.ogi.edu (Iavor S. Diatchki) Date: Mon, 09 Sep 2002 13:45:37 -0700 Subject: mutable records References: <001a01c2531a$a4c5b270$2097fea9@janxp> Message-ID: <3D7D0871.3000407@cse.ogi.edu> hi, > Is it possible to define parts of a record with the help of the *ST s* > monad *mutable* during the whole program? (As is possible in Ocamel)? you can find an example of how to do that at: http://icfpcontest.cse.ogi.edu/simulator/ look inside module Robo for example. there you will find examples of records with mutable fields and some useful functions to manipulate them. the state of the "objects" is not hidden so it is available for anyone to modify. to hide the state you could use fancy types as people already pointed out, or you could use the Haskell module system. unfortunatelly with the Haskell module system approach you soon run into recursive modules (when objects depend on each other) and this is not well supported by Haskell implementations at the moment. bye iavor -- ================================================== | Iavor S. Diatchki, Ph.D. student | | Department of Computer Science and Engineering | | School of OGI at OHSU | | http://www.cse.ogi.edu/~diatchki | ================================================== From jscott@planetinternet.be Tue Sep 10 14:17:07 2002 From: jscott@planetinternet.be (Scott J,) Date: Tue, 10 Sep 2002 15:17:07 +0200 Subject: mutable records References: <001a01c2531a$a4c5b270$2097fea9@janxp> <3D7D0871.3000407@cse.ogi.edu> Message-ID: <002901c258cc$5d3ff340$0100a8c0@janxp> This is a multi-part message in MIME format. ------=_NextPart_000_0025_01C258DD.20593890 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Hi, thx for this reply. Is there any overhead using this mutable? Are you also using Templates ? With this mutable I can adapt a lot of software from Ocamel. But the gnawing question remains: Shall it be possible to be almost as efficient (in native code) as Ocamel's code, I refer here to Doug Bagley's comparison of programming languages. Remarkably the fibonacci numbers test scores almost as well. But the code is not the same. Comparable code would have been to use the same code of Ocamel, to be more specific: how efficiently is recusivity implemented in Haskell. I cannot compare this on my Windows XP since I need MSVC6.0 on this machine which I don't have. On the other hand I have cygwin installed now. Unfortunately I can't make makefiles. Probably on the web I can find an explanation. In this way I can recompile Ocamel with Cygwin and compare the results a bit. There are also 5(?) failures of Haskell programms . Is there a flaw in these programms? Thx Scott P.S. does anyone know a good Haskell IDE for Windows XP? ----- Original Message ----- From: Iavor S. Diatchki Cc: haskell-cafe@haskell.org Sent: Monday, September 09, 2002 10:45 PM Subject: Re: mutable records hi, > Is it possible to define parts of a record with the help of the *ST s* > monad *mutable* during the whole program? (As is possible in Ocamel)? you can find an example of how to do that at: http://icfpcontest.cse.ogi.edu/simulator/ look inside module Robo for example. there you will find examples of records with mutable fields and some useful functions to manipulate them. the state of the "objects" is not hidden so it is available for anyone to modify. to hide the state you could use fancy types as people already pointed out, or you could use the Haskell module system. unfortunatelly with the Haskell module system approach you soon run into recursive modules (when objects depend on each other) and this is not well supported by Haskell implementations at the moment. bye iavor -- ================================================== | Iavor S. Diatchki, Ph.D. student | | Department of Computer Science and Engineering | | School of OGI at OHSU | | http://www.cse.ogi.edu/~diatchki | ================================================== _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ------=_NextPart_000_0025_01C258DD.20593890 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

Hi,

thx for this reply.

Is there any overhead using this=20 mutable?

Are you also using Templates = ?

With this mutable I can adapt a lot of = software=20 from Ocamel.

But the gnawing question remains: Shall = it be=20 possible to be almost as efficient (in native code) as Ocamel's code, I = refer=20 here to Doug Bagley's comparison of programming languages. Remarkably = the=20 fibonacci numbers test scores almost as well. But the code is not the = same.=20 Comparable code would have been to use the same code of Ocamel, to be = more=20 specific: how efficiently is recusivity implemented in Haskell. I cannot = compare=20 this on my Windows XP since I need MSVC6.0 on this machine which I don't = have.=20 On the other hand I have cygwin installed now. Unfortunately I can't = make=20 makefiles. Probably on the web I can find an explanation. In this way I = can=20 recompile Ocamel with Cygwin and compare the results a bit.

There are also 5(?) failures of Haskell = programms .=20 Is there a flaw in these programms?

Thx

Scott

P.S. does anyone know a good = Haskell IDE for=20 Windows XP?

----- Original Message -----

From:=20 Iavor S.=20 Diatchki

Cc: haskell-cafe@haskell.org =

Sent: Monday, September 09, = 2002 10:45=20 PM

Subject: Re: mutable = records

hi,

> Is it possible to define parts of a=20 record with the help of the *ST s*
> monad *mutable* = during the=20 whole program? (As is possible in Ocamel)?

you can find an = example of=20 how to do that at:
http://icfpcontest.cse= .ogi.edu/simulator/

look=20 inside module Robo for example. there you will find examples of=20
records with mutable fields and some useful functions to = manipulate=20
them. the state of the "objects" is not hidden so it is = available=20 for
anyone to modify. to hide the state you could use fancy = types as=20 people
already pointed out, or you could use the Haskell module = system.=20
unfortunatelly with the Haskell module system approach you soon = run into=20
recursive modules (when objects depend on each other) and this is = not=20
well supported by Haskell implementations at the=20 moment.

bye
iavor

--=20 =
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D
| Iavor S. Diatchki,=20 Ph.D.=20 = student           =    =20 |
| Department of Computer Science and Engineering |
| School of = OGI at=20 = OHSU           &nb= sp;           &nbs= p; =20 |
| http://www.cse.ogi.edu/~diatchk= i           &n= bsp;  =20 = |
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D

_______________________________________________
Haskell-= Cafe=20 mailing list
Haskell-Cafe@haskell.org
= http://www.= haskell.org/mailman/listinfo/haskell-cafe
------=_NextPart_000_0025_01C258DD.20593890-- From jadrian@mat.uc.pt Tue Sep 10 15:11:30 2002 From: jadrian@mat.uc.pt (Jorge Adriano) Date: Tue, 10 Sep 2002 15:11:30 +0100 Subject: mutable records In-Reply-To: <002901c258cc$5d3ff340$0100a8c0@janxp> References: <001a01c2531a$a4c5b270$2097fea9@janxp> <3D7D0871.3000407@cse.ogi.edu> <002901c258cc$5d3ff340$0100a8c0@janxp> Message-ID: <200209101511.30033.jadrian@mat.uc.pt> > Hi, > thx for this reply. > Is there any overhead using this mutable? I just thought I should point out that "Mutable" is not an haskell type. You can see in the Utils module that it is just a type synonim for IORef: http://icfpcontest.cse.ogi.edu/simulator/pfe.cgi?Utils#Mutable http://haskell.cs.yale.edu/ghc/docs/latest/html/base/Data.STRef.html I think that sometimes STRef might be a better choice... > Are you also using Templates ? > With this mutable I can adapt a lot of software from Ocamel. I think this John Hughes paper "Global Variables in Haskell" might be use= full=20 to you: http://www.math.chalmers.se/~rjmh/Globals.ps > But the gnawing question remains: Shall it be possible to be almost as > efficient (in native code) as Ocamel's code, I refer here to Doug Bagle= y's > comparison of programming languages. Remarkably the fibonacci numbers t= est > scores almost as well. But the code is not the same. Comparable code wo= uld > have been to use the same code of Ocamel, to be more specific: how > efficiently is recusivity implemented in Haskell. I cannot compare this= on > my Windows XP since I need MSVC6.0 on this machine which I don't have. = On > the other hand I have cygwin installed now. Unfortunately I can't make > makefiles. Probably on the web I can find an explanation. In this way I= can > recompile Ocamel with Cygwin and compare the results a bit. > There are also 5(?) failures of Haskell programms . Is there a flaw in > these programms? > P.S. does anyone know a good Haskell IDE for Windows XP? I don't really use windows but I know there is support for the windows ve= rsion=20 of JCreator: http://www.students.cs.uu.nl/people/rjchaaft/JCreator/ You can always use Xemacs :) http://www.xemacs.org/Download/win32/ http://www.haskell.org/haskell-mode/ J.A. From info@teknosoftbilgi.com Tue Sep 10 17:56:14 2002 From: info@teknosoftbilgi.com (info) Date: Tue, 10 Sep 2002 18:56:14 +0200 Subject: Bilgi Payla�t�k�a Artar Message-ID:

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From nyslik@yahoo.com Fri Sep 13 01:19:52 2002 From: nyslik@yahoo.com (Your Friend) Date: Thu, 12 Sep 2002 20:19:52 -0400 Subject: Make $20,000 with PayPal! Fast, reliable,FREE!!! Message-ID: <200209122004181.SM01328@patil> This is a multi-part message in MIME format --=_NextPart_2rfkindysadvnqw3nerasdf Content-Type: text/plain;charset="windows-1252" Content-Transfer-Encoding: quoted-printable =20 --=_NextPart_2rfkindysadvnqw3nerasdf Content-Type: text/html;windows-1252" Content-Transfer-Encoding: quoted-printable <=21DOCTYPE HTML PUBLIC =22-//W3C//DTD HTML 4.0 Transitional//EN=22>

--=_NextPart_2rfkindysadvnqw3nerasdf-- From nunopedrosilva@yahoo.com Fri Sep 13 15:42:45 2002 From: nunopedrosilva@yahoo.com (Nuno Silva) Date: Fri, 13 Sep 2002 07:42:45 -0700 (PDT) Subject: maxList Message-ID: <20020913144245.31167.qmail@web14605.mail.yahoo.com> --0-1537142547-1031928165=:31160 Content-Type: text/plain; charset=us-ascii hello, I'm new to haskell, I'm studying for an exam, and I'm having trouble with this exercise. I have a list of Integers, and I want to return the highest value of all. i have this: comp :: Int -> Int -> Int comp x y | x < y = y | otherwise = x maxList :: [Int] -> [Int] maxList (x1:x2:xs) = comp x1 x2 : maxList xs maxList [] = [] this code returns a list, but I only want it to return a single Int... but can't seem to do it, could you please help me? --------------------------------- Do you Yahoo!? Yahoo! News - Today's headlines --0-1537142547-1031928165=:31160 Content-Type: text/html; charset=us-ascii

hello, I'm new to haskell, I'm studying for an exam, and I'm having trouble with this exercise.

I have a list of Integers, and I want to return the highest value of all.

i have this:

comp :: Int -> Int -> Int

comp x y | x < y = y

| otherwise = x

maxList :: [Int] -> [Int]

maxList (x1:x2:xs) = comp x1 x2 : maxList xs

maxList [] = []

this code returns a list, but I only want it to return a single Int... but can't seem to do it, could you please help me?

Do you Yahoo!?
Yahoo! News - Today's headlines --0-1537142547-1031928165=:31160-- From hdaume@ISI.EDU Fri Sep 13 15:45:33 2002 From: hdaume@ISI.EDU (Hal Daume III) Date: Fri, 13 Sep 2002 07:45:33 -0700 (PDT) Subject: maxList In-Reply-To: <20020913144245.31167.qmail@web14605.mail.yahoo.com> Message-ID: Hi, > I have a list of Integers, and I want to return the highest value of all. > > i have this: > comp :: Int -> Int -> Int > comp x y | x < y = y > | otherwise = x This looks fine. > maxList :: [Int] -> [Int] This type is probably wrong. If you are only trying to find the single greatest integer, why are you returning a list? Possibly to handle the case when the input list is empty, but a 'Maybe' might be better suited for this (or simply throwing an error). > maxList (x1:x2:xs) = comp x1 x2 : maxList xs > maxList [] = [] You should probably try to think inductively about this problem. Suppose you're given an empty list. What is the maximum value of this list? Well, nothing. This should be an error. Now, suppose you're given a list with only one element. Obviously this single element is the maximum of the list, so you should return it. Suppose you have more than one element. How does the maximum value of the entire list relate to the maximum value of the tail of the list and the head of the list (inductively)? Given that answer, you should be able to write a three line solution. Now, for extra credit, write a one line solution using a fold and your comp function. - Hal (note that your 'comp' function is the standard prelude 'max' function, for the most part, and that your 'maxList' is the prelude 'maximum' function.) From rmb@barthfamily.com Fri Sep 13 20:12:02 2002 From: rmb@barthfamily.com (Richard Barth) Date: Fri, 13 Sep 2002 12:12:02 -0700 Subject: (no subject) Message-ID: <001b01c25b59$776aa550$905af142@l1000> This is a multi-part message in MIME format. ------=_NextPart_000_001C_01C25B1E.CB0BCD50 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit I'm just learning Haskell with Hugs98. I can't understand why the line defining "foo" is acceptable while the line defining "bar" (only difference is the unary minus) generates the error message at the end. If someone could explain this, or, better yet, tell me how I can figure this out for myself. Thanks. data Entry = Ent {date :: String, amount :: Double} foo = [Ent "baz" 1.0] bar = [Ent "baz" -1.0] Type checking...... ERROR "...test.hs":7 - Unresolved top-level overloading *** Binding : bar *** Outstanding context : Fractional (Double -> Entry) ------=_NextPart_000_001C_01C25B1E.CB0BCD50 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

I’m just learning Haskell with Hugs98. I = can’t understand why the line defining “foo” is acceptable while = the line defining “bar” (only difference is the unary minus) = generates the error message at the end. If someone could explain this, or, better yet, = tell me how I can figure this out for myself. = Thanks.

data Entry =3D Ent {date :: String, amount :: Double}

foo =3D [Ent "baz" = 1.0]

bar =3D [Ent "baz" -1.0]

Type checking......

ERROR "...test.hs":7 - Unresolved top-level overloading

*** Binding &nbs= p; : bar

*** Outstanding context : Fractional (Double -> Entry)

------=_NextPart_000_001C_01C25B1E.CB0BCD50-- From ashley@semantic.org Fri Sep 13 20:18:38 2002 From: ashley@semantic.org (Ashley Yakeley) Date: Fri, 13 Sep 2002 12:18:38 -0700 Subject: (no subject) Message-ID: <200209131918.MAA27619@mail4.halcyon.com> At 2002-09-13 12:12, Richard Barth wrote: >I'm just learning Haskell with Hugs98. I can't understand why the line >defining "foo" is acceptable while the line defining "bar" (only >difference is the unary minus) generates the error message at the end. >If someone could explain this, or, better yet, tell me how I can figure >this out for myself. Thanks. > >data Entry = Ent {date :: String, amount :: Double} >foo = [Ent "baz" 1.0] >bar = [Ent "baz" -1.0] Haskell thinks it's a binary minus. Try this: bar = [Ent "baz" (-1.0)] -- Ashley Yakeley, Seattle WA From glynn.clements@virgin.net Fri Sep 13 20:17:10 2002 From: glynn.clements@virgin.net (Glynn Clements) Date: Fri, 13 Sep 2002 20:17:10 +0100 Subject: (no subject) In-Reply-To: <001b01c25b59$776aa550$905af142@l1000> References: <001b01c25b59$776aa550$905af142@l1000> Message-ID: <15746.14774.133598.924417@cerise.nosuchdomain.co.uk> Richard Barth wrote: > I'm just learning Haskell with Hugs98. I can't understand why the line > defining "foo" is acceptable while the line defining "bar" (only > difference is the unary minus) generates the error message at the end. > If someone could explain this, or, better yet, tell me how I can figure > this out for myself. Thanks. > > data Entry = Ent {date :: String, amount :: Double} > foo = [Ent "baz" 1.0] > bar = [Ent "baz" -1.0] bar = [Ent "baz" (-1.0)] A "-" is normally interpreted as the binary subtraction operator rather than the unary negation operator. Most of the time, negative literals need to be enclosed in parentheses. -- Glynn Clements From ham@cs.utexas.edu Fri Sep 13 20:39:28 2002 From: ham@cs.utexas.edu (Hamilton Richards) Date: Fri, 13 Sep 2002 14:39:28 -0500 Subject: (no subject) In-Reply-To: <001b01c25b59$776aa550$905af142@l1000> References: <001b01c25b59$776aa550$905af142@l1000> Message-ID: At 12:12 PM -0700 9/13/02, Richard Barth wrote: >I'm just learning Haskell with Hugs98. I can't understand why the >line defining "foo" is acceptable while the line defining "bar" >(only difference is the unary minus) generates the error message at >the end. If someone could explain this, or, better yet, tell me how >I can figure this out for myself. Thanks. > > > >data Entry = Ent {date :: String, amount :: Double} > >foo = [Ent "baz" 1.0] > >bar = [Ent "baz" -1.0] > > > >Type checking...... > >ERROR "...test.hs":7 - Unresolved top-level overloading > >*** Binding : bar > >*** Outstanding context : Fractional (Double -> Entry) Recall that function application has a higher priority than all the operators --including unary (-). --Ham -- ------------------------------------------------------------------ Hamilton Richards Department of Computer Sciences Senior Lecturer The University of Texas at Austin 512-471-9525 1 University Station C0500 Taylor Hall 5.138 Austin, Texas 78712-1188 ham@cs.utexas.edu hrichrds@swbell.net ------------------------------------------------------------------ From gkosmidis@epsilon7.gr Wed Sep 18 14:32:35 2002 From: gkosmidis@epsilon7.gr (=?iso-8859-7?B?w+n+8ePv8iDK7/Ps3+Tn8g==?=) Date: Wed, 18 Sep 2002 16:32:35 +0300 Subject: layout problem Message-ID: <008901c25f17$dd549670$6000000a@dbserver> This is a multi-part message in MIME format. ------=_NextPart_000_0086_01C25F30.FEC22340 Content-Type: text/plain; charset="iso-8859-7" Content-Transfer-Encoding: quoted-printable Hello everyone. I have a problem with a assessment. The problem is with the layout. I cannot understand what is wrong. Here is the code module Main where import IO import System import List import Maybe import Char import Numeric type Word=3DString type WordCount=3DInt type WordTup=3D(word,wordCount) type WordList=3D[WordTup] main=3Ddo args<-getArgs textLines<-getText switchArgs args textLines where switchArgs args textLines |(isMemberOf "-f" args) && (isMemberOf "-i" args) =3DprintFreq(sortWordCount(parseLcLine = textLines)) |(isMemberOf "-f" args) =3DprintFreq(sortWordCount (parseLine = textLines)) |(isMemberOf "-i" args) =3DprintFreq(sortWordCount (parseLcLine = textLines)) |otherwise =3DprintFreq(sortName (parseLine textLines)) getText::IO String getText=3Ddo c<-getChar e<-isEOF if (e) then return "" else (do nc<-getText return (:nc)) parseLine::String->Wordlist parseLine line |(line/=3D"")&&(isWantedChar (headline)) =3DfillWordList w(parseLine newLine) |(line/=3D"")&&(not(isWantedChar (headline))) =3DparseLine(tail line) isMemberOf::String->[String]->Bool isMemberOf arg args=20 =3D[]/=3D[a|a<-args,a=3D=3Darg] printFreq::WordList->IO() printFreq wl=3Ddo sequence (map putWordStat wl) where=20 putWordStat(Word,WordCount)->IO() putWordStat(w,wc) do putStr w putSpc (20 (length w) (length(show wc))) putStr (show wc) putSpc 8 putStr (showFFloat (Just 2) (fromIntegral = (wc) * 100.0/fromIntegral (wLength))"") putChar '%' putChar '\n' return() wlLength-countWords wl; putSpc::Int->IO() putSpc n |n>1 do putChar '' putSpc (n-1) return() |otherwise=3DputChar '' countWords:Wordlist->Int countWords [ ] countWords ((w,wc):wl)=3Dwc+countWords wl sortName::WordList->WordList sortName [ ] =3D [ ]=20 sortName (wn:ws)=3DsortName [(w,wc) (w,wc) <-ws,not (isGreater = (w,wc)wc)] ++[wn]++sortName[(w,wc)|(w,wc)<-ws, isGreater (w,wc) = wn] where isGreater (wl,wcl) (w2,wc2) |ord(head(wl))-ord(head(x2))>0=3DTrue |ord(head(wl))-ord(head(x2))<0=3DFalse |length wl>l && length w2>l =3DisGreater(tail(wl),wcl) (tail(w2,wc2) |otherwise =3D [] where w=3DparseWord line newline=3Ddrop (length w) line parseLcLine::String->WordList parseLcLine line |(line/=3D"") && (isWantedChar (head = line))=3DfillWordList w (parseLcLine newline) |(line/=3D"") && (not (isWantedChar (head = line)))=3DparseLcLine (tail line) |otherwise =3D [] where w=3Dmap toLower (parseWord line) newline=3Ddrop (lenfth w) line parseWord::Word->Word parseWord w |(w/=3D"") && (isWantedChar (head w))=3D(head w): = parseWord (tail w)) |otherwise =3D "" isWantedChar::Char->Bool isWantedChar c | (c=3D=3D'a'|| c=3D=3D'b'|| c=3D=3D'c'|| = c=3D=3D'd'|| c=3D=3D'e'|| c=3D=3D'f'|| c=3D=3D'g'|| c=3D=3D'h'|| = c=3D=3D'i'|| c=3D=3D'j'|| c=3D=3D'k'|| c=3D=3D'l'|| c=3D=3D'm'|| = c=3D=3D'n'|| c=3D=3D'o'|| c=3D=3D'p'|| c=3D=3D'q'|| c=3D=3D'r'|| = c=3D=3D's'|| c=3D=3D't'|| c=3D=3D'u'|| c=3D=3D'v'|| c=3D=3D'w'|| = c=3D=3D'x'|| c=3D=3D'y'|| c=3D=3D'z'||c=3D=3D'A'|| c=3D=3D'B'|| = c=3D=3D'C'|| c=3D=3D'D'|| c=3D=3D'E'|| c=3D=3D'F'|| c=3D=3D'G'|| = c=3D=3D'H'|| c=3D=3D'I'|| c=3D=3D'J'|| c=3D=3D'K'|| c=3D=3D'L'|| = c=3D=3D'M'|| c=3D=3D'N'|| c=3D=3D'O'|| c=3D=3D'P'|| c=3D=3D'Q'|| = c=3D=3D'R'|| c=3D=3D'S'|| c=3D=3D'T'|| c=3D=3D'U'|| c=3D=3D'V'|| = c=3D=3D'W'|| c=3D=3D'X'|| c=3D=3D'Y'|| c=3D=3D'Z'|| =3D True) |otherwise =3D False fillWordList::Word->WordList->WordList fillWordList w wordlistl |cWord/=3D [] = =3DcWord++[wordl,wordCountl)|(wordl,wordCountl<-wordListl,wordl/=3Dw] |otherwise =3D (w,l):wordListl where cWord=3D[(wordl,(wordCountl-l)) | = (wordl,wordCountl)<-wordListl,wordl=3D=3Dw] |length w1>1 && length = w2=3D=3D1=3DTrue |otherwise =3D False sortWordCount::WordList->WordList sortWordCount [] =3D [] sortWordCount ((wn,wcn):ws=3DsortWordCount = [(w,wc|cw,wc)<-ws,ws<=3Dwvn++=20 [(wn,wcn)]++sortWordCount = [(cw,wc)|(w,wc)<-ws,wcs,wcn] ------=_NextPart_000_0086_01C25F30.FEC22340 Content-Type: text/html; charset="iso-8859-7" Content-Transfer-Encoding: quoted-printable

Hello=20 everyone.

I have a = problem with a=20 assessment.

The problem = is with the=20 layout.

I cannot = understand what is=20 wrong.

Here is the=20 code

module Main = where
import=20 IO
import System
import List
import Maybe
import = Char
import=20 Numeric

type = Word=3DString
type=20 WordCount=3DInt
type WordTup=3D(word,wordCount)
type=20 WordList=3D[WordTup]

main=3Ddo=20 args<-getArgs
       =20 textLines<-getText
        = switchArgs=20 args textLines
       =20 where
        switchArgs args=20 textLines
          = |(isMemberOf=20 "-f" args) && (isMemberOf "-i"=20 args)
          &nbs= p;            = ; =20 =3DprintFreq(sortWordCount(parseLcLine=20 textLines))
         &nbs= p;            = ; =20 |(isMemberOf "-f"=20 args)
          &nbs= p;            = ; =20 =3DprintFreq(sortWordCount (parseLine=20 textLines))
         &nbs= p;            = ; =20 |(isMemberOf "-i"=20 args)
          &nbs= p;            = ; =20 =3DprintFreq(sortWordCount (parseLcLine=20 textLines))
         &nbs= p;            = ; =20 |otherwise
          = ;            =   =20 =3DprintFreq(sortName (parseLine=20 textLines))
        getText::IO=20 String
        getText=3Ddo=20 c<-getChar
         &n= bsp;        =20 e<-isEOF
         &nbs= p;        =20 if=20 (e)
           =     =20 then return ""=20 else
           = ;           =20 (do=20 nc<-getText
         &= nbsp;           &n= bsp;    =20 return (:nc))
       =20 parseLine::String->Wordlist
      &nb= sp;=20 parseLine=20 line
           = ;      =20 |(line/=3D"")&&(isWantedChar=20 (headline))
         &nbs= p;        =20 =3DfillWordList w(parseLine=20 newLine)
          &= nbsp;      =20 |(line/=3D"")&&(not(isWantedChar=20 (headline)))
         &nb= sp;        =20 =3DparseLine(tail line)

       =20 isMemberOf::String->[String]->Bool
     = ;  =20 isMemberOf arg args=20
           &nb= sp;      =20 =3D[]/=3D[a|a<-args,a=3D=3Darg]

       =20 printFreq::WordList->IO()
       = ;=20 printFreq wl=3Ddo sequence (map putWordStat=20 wl)
           =              = where=20
           &nb= sp;           =20 putWordStat(Word,WordCount)->IO()
     &nb= sp;           &nbs= p;     =20 putWordStat(w,wc)
        &nbs= p;            = ;  =20 do putStr=20 w
           &n= bsp;           &nb= sp;  =20 putSpc (20 (length w) (length(show=20 wc)))
          &nbs= p;            = ;   =20 putStr (show=20 wc)
           =             &= nbsp;  =20 putSpc=20 8
           &n= bsp;           &nb= sp;  =20 putStr (showFFloat (Just 2) (fromIntegral (wc) * 100.0/fromIntegral=20 (wLength))"")
         &n= bsp;           &nb= sp;    =20 putChar=20 '%'
           =             &= nbsp;  =20 putChar=20 '\n'
           = ;            = =20 return()
          &= nbsp;           &n= bsp;=20 wlLength-countWords wl;

       =20 putSpc::Int->IO()
        = putSpc=20 n
           &n= bsp;  =20 |n>1 do putChar=20 ''
           &= nbsp;          =20 putSpc=20 (n-1)
          &nbs= p;    =20 return()
          &= nbsp;   =20 |otherwise=3DputChar ''

       =20 countWords:Wordlist->Int
       = =20 countWords [ ]
        countWords=20 ((w,wc):wl)=3Dwc+countWords = wl
       =20 sortName::WordList->WordList
      &n= bsp;=20 sortName [ ] =3D [ ]
        = sortName=20 (wn:ws)=3DsortName [(w,wc) (w,wc) <-ws,not (isGreater=20 (w,wc)wc)]
          = ;       =20 ++[wn]++sortName[(w,wc)|(w,wc)<-ws, isGreater (w,wc)=20 wn]
           =       =20 where
          &nbs= p;      =20 isGreater (wl,wcl)=20 (w2,wc2)
          &= nbsp;           &n= bsp;     =20 |ord(head(wl))-ord(head(x2))>0=3DTrue
     = ;            =            =20 |ord(head(wl))-ord(head(x2))<0=3DFalse
    &nbs= p;            = ;           =20 |length wl>l && length=20 w2>l
          &n= bsp;           &nb= sp;      =20 =3DisGreater(tail(wl),wcl)=20 (tail(w2,wc2)
         &n= bsp;           &nb= sp;      =20 |otherwise =3D=20 []
           &= nbsp;           &n= bsp;    =20 where
          &nbs= p;            = ;     =20 w=3DparseWord=20 line
           = ;            =      =20 newline=3Ddrop (length w) = line
       =20 parseLcLine::String->WordList
      &= nbsp;=20 parseLcLine=20 line
           = ;        =20 |(line/=3D””) && (isWantedChar (head = line))=3DfillWordList w (parseLcLine=20 newline)
          &= nbsp;        =20 |(line/=3D””) && (not (isWantedChar (head = line)))=3DparseLcLine (tail=20 line)
          &nbs= p;        =20 |otherwise =3D=20 []
           &= nbsp;       =20 where
          &nbs= p;        =20 w=3Dmap toLower (parseWord=20 line)
          &nbs= p;        =20 newline=3Ddrop (lenfth w) = line
       =20 parseWord::Word->Word
        = parseWord=20 w
           &n= bsp;     =20 |(w/=3D””) && (isWantedChar (head w))=3D(head w): = parseWord (tail=20 w))
           =       =20 |otherwise =3D “”

       =20 isWantedChar::Char->Bool
       = =20 isWantedChar=20 c
           &n= bsp;        =20 | (c=3D=3D’a’|| c=3D=3D’b’|| = c=3D=3D’c’|| c=3D=3D’d’|| = c=3D=3D’e’|| c=3D=3D’f’|| = c=3D=3D’g’|| c=3D=3D’h’||=20 c=3D=3D’i’|| c=3D=3D’j’|| = c=3D=3D’k’|| c=3D=3D’l’|| = c=3D=3D’m’|| c=3D=3D’n’|| = c=3D=3D’o’|| c=3D=3D’p’||=20 c=3D=3D’q’|| c=3D=3D’r’|| = c=3D=3D’s’|| c=3D=3D’t’|| = c=3D=3D’u’|| c=3D=3D’v’|| = c=3D=3D’w’|| c=3D=3D’x’|| = c=3D=3D’y’||=20 c=3D=3D’z’||c=3D=3D’A’|| = c=3D=3D’B’|| c=3D=3D’C’|| = c=3D=3D’D’|| c=3D=3D’E’|| = c=3D=3D’F’|| c=3D=3D’G’|| = c=3D=3D’H’||=20 c=3D=3D’I’|| c=3D=3D’J’|| = c=3D=3D’K’|| c=3D=3D’L’|| = c=3D=3D’M’|| c=3D=3D’N’|| = c=3D=3D’O’|| c=3D=3D’P’||=20 c=3D=3D’Q’|| c=3D=3D’R’|| = c=3D=3D’S’|| c=3D=3D’T’|| = c=3D=3D’U’|| c=3D=3D’V’|| = c=3D=3D’W’|| c=3D=3D’X’|| = c=3D=3D’Y’||=20 c=3D=3D’Z’|| =3D=20 True)
          &nbs= p;         =20 |otherwise =3D False
      =20 fillWordList::Word->WordList->WordList
    &= nbsp; =20 fillWordList w=20 wordlistl
          =          =20 |cWord/=3D []=20 =3DcWord++[wordl,wordCountl)|(wordl,wordCountl<-wordListl,wordl/=3Dw]<= BR>           &nbs= p;       =20 |otherwise =3D=20 (w,l):wordListl
         =           =20 where
          &nbs= p;        =20 cWord=3D[(wordl,(wordCountl-l)) |=20 (wordl,wordCountl)<-wordListl,wordl=3D=3Dw]
    = ;            =             &= nbsp;           &n= bsp;        =20 |length w1>1 && length=20 w2=3D=3D1=3DTrue
         = ;            =             &= nbsp;           &n= bsp;   =20 |otherwise =3D False
       =20 sortWordCount::WordList->WordList
     &nb= sp; =20 sortWordCount [] =3D []
       =20 sortWordCount ((wn,wcn):ws=3DsortWordCount = [(w,wc|cw,wc)<-ws,ws<=3Dwvn++=20
           &nb= sp;          =20 [(wn,wcn)]++sortWordCount = [(cw,wc)|(w,wc)<-ws,wcs,wcn]

------=_NextPart_000_0086_01C25F30.FEC22340-- From hdaume@ISI.EDU Wed Sep 18 15:34:42 2002 From: hdaume@ISI.EDU (Hal Daume III) Date: Wed, 18 Sep 2002 07:34:42 -0700 (PDT) Subject: layout problem In-Reply-To: <008901c25f17$dd549670$6000000a@dbserver> Message-ID: > |(isMemberOf "-f" args) && (isMemberOf "-i" args) > =printFreq(sortWordCount(parseLcLine textLines)) > |(isMemberOf "-f" args) these two '|'s should be lined up, as in: > |(isMemberOf "-f" args) && (isMemberOf "-i" args) > =printFreq(sortWordCount(parseLcLine textLines)) > |(isMemberOf "-f" args) as should all successive '|'s From gkosmidis@epsilon7.gr Thu Sep 19 08:19:57 2002 From: gkosmidis@epsilon7.gr (=?iso-8859-7?B?w+n+8ePv8iDK7/Ps3+Tn8g==?=) Date: Thu, 19 Sep 2002 10:19:57 +0300 Subject: layout problem References: <20020918160103.9F2AC4223C1@www.haskell.org> Message-ID: <001301c25fac$fbdddcb0$6000000a@dbserver> Thanks for your answer. The lines where as you asnwered me. When I post my mail the layout was tottally ruined. Here I post the program again but I have replaced all spaces with underscores ( _ ) This is the error that I have: ERROR "c:\textanalysis.HS":48 - Syntax error in declaration (unexpected `->') Thanks in advance for all the help that you can give me module Main where import IO import System import List import Maybe import Char import Numeric type Word=String type WordCount=Int type WordTup=(word,wordCount) type WordList=[WordTup] main=do args<-getArgs ________textLines<-getText ________switchArgs args textLines ________where ________switchArgs args textLines ________________________|(isMemberOf "-f" args) && (isMemberOf "-i" args) _________________________=printFreq(sortWordCount(parseLcLine textLines)) ________________________|(isMemberOf "-f" args) _________________________=printFreq(sortWordCount (parseLine textLines)) ________________________|(isMemberOf "-i" args) _________________________=printFreq(sortWordCount (parseLcLine textLines)) ________________________|otherwise _________________________=printFreq(sortName (parseLine textLines)) ________getText::IO String ________getText=do c<-getChar ___________________e<-isEOF ___________________if (e) _______________________then return "" else _______________________(do nc<-getText ___________________________return (:nc)) ________parseLine::String->Wordlist ________parseLine line __________________|(line/="")&&(isWantedChar (headline)) ___________________=fillWordList w(parseLine newLine) __________________|(line/="")&&(not(isWantedChar (headline))) ___________________=parseLine(tail line) ________isMemberOf::String->[String]->Bool ________isMemberOf arg args ___________________=[]/=[a|a<-args,a==arg] ________printFreq::WordList->IO() ________printFreq wl=do sequence (map putWordStat wl) ________________________where ________________________putWordStat(Word,WordCount)->IO() ________________________putWordStat(w,wc) ________________________do putStr w ___________________________putSpc (20 (length w) (length(show wc))) ___________________________putStr (show wc) ___________________________putSpc 8 ___________________________putStr (showFFloat (Just 2) (fromIntegral (wc) * 100.0/fromIntegral (wLength))"") ___________________________putChar '%' ___________________________putChar '\n' ________________________return() ________________________wlLength-countWords wl; ________putSpc::Int->IO() ________putSpc n _______________|n>1 do putChar '' _______________________putSpc (n-1) ________________return() _______________|otherwise=putChar '' ________countWords:Wordlist->Int ________countWords [ ] ________countWords ((w,wc):wl)=wc+countWords wl ________sortName::WordList->WordList ________sortName [ ] = [ ] ________sortName (wn:ws)=sortName [(w,wc) (w,wc) <-ws,not (isGreater (w,wc)wc)] __________________++[wn]++sortName[(w,wc)|(w,wc)<-ws, isGreater (w,wc) wn] __________________where __________________isGreater (wl,wcl) (w2,wc2) _____________________________|ord(head(wl))-ord(head(x2))>0=True _____________________________|ord(head(wl))-ord(head(x2))<0=False _____________________________|length wl>l && length w2>l ______________________________=isGreater(tail(wl),wcl) (tail(w2,wc2) _____________________________|otherwise = [] _____________________________where _____________________________w=parseWord line _____________________________newline=drop (length w) line ________parseLcLine::String->WordList ________parseLcLine line ____________________|(line/="") && (isWantedChar (head line))=fillWordList w (parseLcLine newline) ____________________|(line/="") && (not (isWantedChar (head line)))=parseLcLine (tail line) ____________________|otherwise = [] ____________________where ____________________w=map toLower (parseWord line) ____________________newline=drop (lenfth w) line ________parseWord::Word->Word ________parseWord w __________________|(w/="") && (isWantedChar (head w))=(head w): parseWord (tail w)) __________________|otherwise = "" ________isWantedChar::Char->Bool ________isWantedChar c _____________________| (c=='a'|| c=='b'|| c=='c'|| c=='d'|| c=='e'|| c=='f' || c=='g'|| c=='h'|| c=='i'||__c=='j'|| c=='k'|| c=='l'|| c=='m'|| c=='n'|| c=='o'|| c=='p'|| c=='q'|| c=='r'|| c=='s'|| c=='t'|| c=='u'|| c=='v'|| c==' w'|| c=='x'|| c=='y'|| c=='z'||c=='A'|| c=='B'|| c=='C'|| c=='D'|| c=='E'|| c=='F'|| c=='G'|| c=='H'|| c=='I'||__c=='J'|| c=='K'|| c=='L'|| c=='M'|| c== 'N'|| c=='O'|| c=='P'|| c=='Q'|| c=='R'|| c=='S'|| c=='T'|| c=='U'|| c=='V' || c=='W'|| c=='X'|| c=='Y'|| c=='Z'|| = True) _____________________|otherwise = False _______fillWordList::Word->WordList->WordList _______fillWordList w wordlistl ____________________|cWord/= [] =cWord++[wordl,wordCountl)|(wordl,wordCountl<-wordListl,wordl/=w] ____________________|otherwise = (w,l):wordListl ____________________where ____________________cWord=[(wordl,(wordCountl-l)) | (wordl,wordCountl)<-wordListl,wordl==w] __________________________________________________|length w1>1 && length w2==1=True __________________________________________________|otherwise = False ________sortWordCount::WordList->WordList ________sortWordCount [] = [] ________sortWordCount ((wn,wcn):ws=sortWordCount [(w,wc|cw,wc)<-ws,ws<=wvn++ _______________________[(wn,wcn)]++sortWordCount [(cw,wc)|(w,wc)<-ws,wcs,wcn] From Malcolm.Wallace@cs.york.ac.uk Thu Sep 19 13:49:15 2002 From: Malcolm.Wallace@cs.york.ac.uk (Malcolm Wallace) Date: Thu, 19 Sep 2002 13:49:15 +0100 Subject: layout problem In-Reply-To: <001301c25fac$fbdddcb0$6000000a@dbserver> References: <20020918160103.9F2AC4223C1@www.haskell.org> <001301c25fac$fbdddcb0$6000000a@dbserver> Message-ID: <20020919134915.5c7190f4.Malcolm.Wallace@cs.york.ac.uk> "�� " writes: > This is the error that I have: ERROR "c:\textanalysis.HS":48 - Syntax > error in declaration (unexpected `->') Line 48: > ________________________putWordStat(Word,WordCount)->IO() There is a :: missing between the function name and its type. > ________________________putWordStat::(Word,WordCount)->IO() The function definition is also missing an = sign: > ________________________putWordStat(w,wc) > ________________________do should be > ________________________putWordStat(w,wc)= > ________________________do Finally, in this whole block: > ________printFreq wl=do sequence (map putWordStat wl) > ________________________where > ________________________putWordStat::(Word,WordCount)->IO() > ________________________putWordStat(w,wc)= > ________________________do ... > ________________________return() > ________________________wlLength-countWords wl; the indentation is incorrect. You probably meant to write something along these lines: > ________printFreq wl=do sequence (map putWordStat wl) > ____________________________where > ______________________________putWordStat::(Word,WordCount)->IO() > ______________________________putWordStat(w,wc)= > ________________________________do ... > ___________________________________return() > ________________________wlLength-countWords wl; but even this has two faults. First, a `where' clause can only be attached to a whole definition, not to a single statement within a `do'. Second, the final statement of the outer `do' should be a statement e.g. "return (wlLength-countWords wl)", not a simple value. Regards, Malcolm From shiin@gmx.de Thu Sep 19 14:45:51 2002 From: shiin@gmx.de (Dennis Schieferdecker) Date: Thu, 19 Sep 2002 15:45:51 +0200 Subject: Depth-First search problems Message-ID: <3D89D50E.CAC2A717@gmx.de> Hi! I hope you can help me with this little problem I have: I'm trying to implement a depth-first search on a binary tree from a school book but somehow I always get Haskell error messages (more after the source code). The source is as follows: -- Binary Tree structure data BinTree t = EmptyTree | Bin (BinTree t) t (BinTree t) left (Bin b1 _ _) = b1 right (Bin _ _ b2) = b2 value (Bin _ v _) = v empty EmptyTree = True empty (Bin _ _ _) = False -- Give the Binary Tree == instance Eq a => Eq (BinTree a) where (Bin b v c) == (Bin d w e) = (v == w) && (b == d) && (c == e) EmptyTree == EmptyTree = True EmptyTree == Bin _ _ _ = False -- Stack structure data Keller t = CreateStack | Push (Keller t) t top (Push s x) = x pop (Push s x) = s -- Depth-First search tiefensuche b = fst (until p f ([], Push CreateStack b)) where p(_, k) = empty k f(erg, k) | (top k) == EmptyTree = (erg, pop k) | otherwise = ([v] ++ erg, Push( Push( pop k) b2) b1) where (Bin b1 v b2) = top k The error message says that p has a wrong types Haskell thinks it is p :: (b, BinTree c) -> Bool, instead of p :: ([a], Keller (BinTree a)) -> Bool I really don't know how I can tell to see the right type. Does anyone have an idea what I have to change ? -- ciao dennis "I hear and I forget, I see and I remember, I do and I understand" From gkosmidis@epsilon7.gr Thu Sep 19 15:33:24 2002 From: gkosmidis@epsilon7.gr (=?iso-8859-1?Q?G=3F=3F=3F=3F=3F=3F_=3F=3Fs=B5=3Fd=3F=3F?=) Date: Thu, 19 Sep 2002 17:33:24 +0300 Subject: layout problem References: <20020918160103.9F2AC4223C1@www.haskell.org><001301c25fac$fbdddcb0$6000000a@dbserver> <20020919134915.5c7190f4.Malcolm.Wallace@cs.york.ac.uk> Message-ID: <009901c25fe9$86b08810$6000000a@dbserver> at least i passed that line! unfortunatelly i stack again :( This is the error this time. What can i say.I cannot understand the error the compiler returns.it is not much help. ERROR "c:\1.hs":69 - Syntax error in expression (unexpected `<-') module_Main_where import_IO import_System import_List import_Maybe import_Char import_Numeric type_Word=String type_WordCount=Int type_WordTup=(word,wordCount) type_WordList=[WordTup] main=do_args<-getArgs ________textLines<-getText ________switchArgs_args_textLines ________where ________switchArgs_args_textLines ________|(isMemberOf_"-f"_args)_&&_(isMemberOf_"-i"_args) _________________________=printFreq(sortWordCount(parseLcLine_textLines)) ________________________|(isMemberOf_"-f"_args) _________________________=printFreq(sortWordCount_(parseLine_textLines)) ________________________|(isMemberOf_"-i"_args) _________________________=printFreq(sortWordCount_(parseLcLine_textLines)) ________________________|otherwise _________________________=printFreq(sortName_(parseLine_textLines)) ________getText::IO_String ________getText=do_c<-getChar ___________________e<-isEOF ___________________if_(e) _______________then_return_""_else _______________________(do_nc<-getText ___________________________return_(:nc)) ________parseLine::String->Wordlist ________parseLine_line __________________|(line/="")&&(isWantedChar_(headline)) ___________________=fillWordList_w(parseLine_newLine) __________________|(line/="")&&(not(isWantedChar_(headline))) ___________________=parseLine(tail_line) ________isMemberOf::String->[String]->Bool ________isMemberOf_arg_args_ ___________________=[]/=[a|a<-args,a==arg] ________printFreq::WordList->IO() ________printFreq_wl=do_sequence_(map_putWordStat_wl) _________________________________where_ ______________________________________putWordStat::(Word,WordCount)->IO() ______________________________________putWordStat(w,wc)=do_putStr_w ___________________________________________________________putSpc_(20_(lengt h_w)_(length(show_wc))) ___________________________________________________________putStr_(show_wc) ___________________________________________________________putSpc_8 ___________________________________________________________putStr_(showFFloa t_(Just_2)_(fromIntegral_(wc)_*_100.0/fromIntegral_(wLength))"") ___________________________________________________________putChar_'%' ___________________________________________________________putChar_'\n' ___________________________________________________________return(wlLength-c ountWords_wl) ________putSpc::Int->IO() ________putSpc_n _______________|(n>1)_=_do_putChar_'_' ___________________________putSpc_(n-1) ___________________________return() _______________|otherwise_=_putChar_'_' ________countWords::Wordlist->Int ________countWords_[] ____________________countWords_((w,wc):wl)=wc+countWords_wl ________sortName::WordList->WordList ________sortName_[]_=_[]_ ________sortName_(wn:ws)=sortName_[(w,wc)_(w,wc)_<-_ws,not_(isGreater_(w,wc) _wc)] _________________________++[wn]++sortName[(w,wc)|(w,wc)<-ws,_isGreater_(w,wc )_wn] __________________where __________________isGreater_(wl,wcl)_(w2,wc2) _____________________________|ord(head(wl))-ord(head(x2))>0=True _____________________________|ord(head(wl))-ord(head(x2))<0=False _____________________________|length_wl>l_&&_length_w2>l ______________________________=isGreater(tail(wl),wcl)_(tail(w2,wc2) _____________________________|otherwise_=_[] _____________________________where _____________________________w=parseWord_line _____________________________newline=drop_(length_w)_line ________parseLcLine::String->WordList ________parseLcLine_line ____________________|(line/="")_&&_(isWantedChar_(head_line))=fillWordList_w _(parseLcLine_newline) ____________________|(line/="")_&&_(not_(isWantedChar_(head_line)))=parseLcL ine_(tail_line) ____________________|otherwise_=_[] ____________________where ____________________w=map_toLower_(parseWord_line) ____________________newline=drop_(lenfth_w)_line ________parseWord::Word->Word ________parseWord_w __________________|(w/="")_&&_(isWantedChar_(head_w))=(head_w):_parseWord_(t ail_w)) __________________|otherwise_=_"" ________isWantedChar::Char->Bool ________isWantedChar_c _____________________|_(c=='a'||_c=='b'||_c=='c'||_c=='d'||_c=='e'||_c=='f' ||_c=='g'||_c=='h'||_c=='i'||__c=='j'||_c=='k'||_c=='l'||_c=='m'||_c=='n' ||_c=='o'||_c=='p'||_c=='q'||_c=='r'||_c=='s'||_c=='t'||_c=='u'||_c=='v' ||_c=='w'||_c=='x'||_c=='y'||_c=='z'||c=='A'||_c=='B'||_c=='C'||_c=='D' ||_c=='E'||_c=='F'||_c=='G'||_c=='H'||_c=='I'||__c=='J'||_c=='K'||_c=='L' ||_c=='M'||_c=='N'||_c=='O'||_c=='P'||_c=='Q'||_c=='R'||_c=='S'||_c=='T' ||_c=='U'||_c=='V'||_c=='W'||_c=='X'||_c=='Y'||_c=='Z'||_=_True) _____________________|otherwise_=_False _______fillWordList::Word->WordList->WordList _______fillWordList_w_wordlistl ____________________|cWord/=_[]_=cWord++[wordl,wordCountl)|(wordl,wordCountl <-wordListl,wordl/=w] ____________________|otherwise_=_(w,l):wordListl ____________________where ____________________cWord=[(wordl,(wordCountl-l))_|_(wordl,wordCountl)<-word Listl,wordl==w] __________________________________________________|length_w1>1_&&_length_w2= =1=True __________________________________________________|otherwise_=_False ________sortWordCount::WordList->WordList ________sortWordCount_[]_=_[] ________sortWordCount_((wn,wcn):ws=sortWordCount_[(w,wc|cw,wc)<-ws,ws<=wvn++ _ _______________________[(wn,wcn)]++sortWordCount_[(cw,wc)|(w,wc)<-ws,wcs,wcn ] From Malcolm.Wallace@cs.york.ac.uk Thu Sep 19 15:33:26 2002 From: Malcolm.Wallace@cs.york.ac.uk (Malcolm Wallace) Date: Thu, 19 Sep 2002 15:33:26 +0100 Subject: layout problem In-Reply-To: <009901c25fe9$86b08810$6000000a@dbserver> References: <20020918160103.9F2AC4223C1@www.haskell.org> <001301c25fac$fbdddcb0$6000000a@dbserver> <20020919134915.5c7190f4.Malcolm.Wallace@cs.york.ac.uk> <009901c25fe9$86b08810$6000000a@dbserver> Message-ID: <20020919153326.42949bb9.Malcolm.Wallace@cs.york.ac.uk> > ERROR "c:\1.hs":69 - Syntax error in expression (unexpected `<-') Line 69: > sortName (wn:ws)=sortName [(w,wc) (w,wc) <- ws,not (isGreater (w,wc) wc)] > ++[wn]++sortName[(w,wc)|(w,wc)<-ws, isGreater (w,wc) wn] The first list comprehension expression [ (w,wc) (w,wc) <- ... ] is missing a vertical bar, i.e. [ (w,wc) | (w,wc) <- ... ] Regards, Malcolm From paul.hudak@yale.edu Thu Sep 19 15:35:21 2002 From: paul.hudak@yale.edu (Paul Hudak) Date: Thu, 19 Sep 2002 10:35:21 -0400 Subject: Depth-First search problems References: <3D89D50E.CAC2A717@gmx.de> Message-ID: <3D89E0A9.128D1B4E@yale.edu> I'm not sure whether your program is correct, but it's easy to see why you're getting the type error. You define p(_, k) = empty k, but empty has type BinTree t -> Bool, so clearly p has type (a, BinTree t) -> Bool. However, you use p in "until p f ([], Push CreateStack b)". Since until has type (a -> Bool) -> (a -> a) -> a -> a, this implies that p must have type ([a], Keller (BinTree t)) -> Bool. So you need to either fix the definition of p or fix how it is used. By the way, you are missing the case (Bin _ _ _) == EmptyTree in the instance decl. Also, note that Keller t is isomorphic to [t], i.e. to the list data type. Specifically, CreateStack is [], Push is (:), top is head, and pop is tail. Hope this helps, -Paul Hudak > -- Binary Tree structure > data BinTree t = EmptyTree | Bin (BinTree t) t (BinTree t) > left (Bin b1 _ _) = b1 > right (Bin _ _ b2) = b2 > value (Bin _ v _) = v > empty EmptyTree = True > empty (Bin _ _ _) = False > > -- Give the Binary Tree == > instance Eq a => Eq (BinTree a) where > (Bin b v c) == (Bin d w e) = (v == w) && (b == d) && (c == e) > EmptyTree == EmptyTree = True > EmptyTree == Bin _ _ _ = False > > -- Stack structure > data Keller t = CreateStack | Push (Keller t) t > top (Push s x) = x > pop (Push s x) = s > > -- Depth-First search > tiefensuche b = fst (until p f ([], Push CreateStack b)) > where p(_, k) = empty k > f(erg, k) | (top k) == EmptyTree = (erg, pop k) > | otherwise = ([v] ++ erg, Push( Push( pop k) b2) b1) > where (Bin b1 v b2) = top k > > The error message says that p has a wrong types > Haskell thinks it is p :: (b, BinTree c) -> Bool, instead of p :: ([a], > Keller (BinTree a)) -> Bool From shiin@gmx.de Thu Sep 19 18:00:49 2002 From: shiin@gmx.de (Dennis Schieferdecker) Date: Thu, 19 Sep 2002 19:00:49 +0200 Subject: Depth-First search problems References: <3D89D50E.CAC2A717@gmx.de> <3D89E0A9.128D1B4E@yale.edu> Message-ID: <3D8A02C1.BE78C40B@gmx.de> Paul Hudak wrote: > I'm not sure whether your program is correct, but it's easy to see why > you're getting the type error. You define p(_, k) = empty k, but empty > has type BinTree t -> Bool, so clearly p has type (a, BinTree t) -> > Bool. However, you use p in "until p f ([], Push CreateStack b)". > Since until has type (a -> Bool) -> (a -> a) -> a -> a, this implies > that p must have type ([a], Keller (BinTree t)) -> Bool. So you need to > either fix the definition of p or fix how it is used. > > By the way, you are missing the case (Bin _ _ _) == EmptyTree in the > instance decl. Also, note that Keller t is isomorphic to [t], i.e. to > the list data type. Specifically, CreateStack is [], Push is (:), top > is head, and pop is tail. > > Hope this helps, -Paul Hudak Thanks, that really helped. My fault was that the depth-search algorithm expected an empty-method for the stack not for the binary tree. -- ciao dennis "I hear and I forget, I see and I remember, I do and I understand" From nick.name@inwind.it Thu Sep 19 21:06:59 2002 From: nick.name@inwind.it (Nick Name) Date: Thu, 19 Sep 2002 22:06:59 +0200 Subject: "zipping" two streams in the IO monad Message-ID: <20020919220659.622e1a77.nick.name@inwind.it> How could I "zip" two possibily infinite streams obtained by IO operations, for example to return the infinite list of pairs of values read both from channel a and from channel b with getChanContents? In general, how does one implement a function like "getChanContents" wich returns an infinite list? Tell me just some pointer to information of course, I don't want an entire functional programming lesson :) Vincenzo From duncan@coutts.uklinux.net Thu Sep 19 21:28:31 2002 From: duncan@coutts.uklinux.net (Duncan Coutts) Date: Thu, 19 Sep 2002 21:28:31 +0100 Subject: "zipping" two streams in the IO monad In-Reply-To: <20020919220659.622e1a77.nick.name@inwind.it> References: <20020919220659.622e1a77.nick.name@inwind.it> Message-ID: <20020919212831.6b85a225.duncan@coutts.uklinux.net> On Thu, 19 Sep 2002 22:06:59 +0200 Nick Name wrote: > In general, how does one implement a function like "getChanContents" > wich returns an infinite list? Tell me just some pointer to information > of course, I don't want an entire functional programming lesson :) See unsafeInterleaveIO: http://www.haskell.org/ghc/docs/latest/html/base/System.IO.Unsafe.html#unsafeInterleaveIO This is how getContents is implemented so that it reads the file lazily. It is "unsafe" in that it doesn't guarantee any particuar order of evaluation with respect to other IO operations. Duncan From nick.name@inwind.it Thu Sep 19 21:35:25 2002 From: nick.name@inwind.it (Nick Name) Date: Thu, 19 Sep 2002 22:35:25 +0200 Subject: "zipping" two streams in the IO monad In-Reply-To: <20020919212831.6b85a225.duncan@coutts.uklinux.net> References: <20020919220659.622e1a77.nick.name@inwind.it> <20020919212831.6b85a225.duncan@coutts.uklinux.net> Message-ID: <20020919223525.7667575b.nick.name@inwind.it> On Thu, 19 Sep 2002 21:28:31 +0100 Duncan Coutts wrote: > > See unsafeInterleaveIO: Thanks for help, I'm going to look at it. Vincenzo From droundy@civet.berkeley.edu Sat Sep 21 12:30:03 2002 From: droundy@civet.berkeley.edu (David Roundy) Date: Sat, 21 Sep 2002 07:30:03 -0400 Subject: question regarding ordering of function definitions Message-ID: <20020921112937.GA9057@jdj5.mit.edu> Hello all! I've just started learning (and using haskell), and am also using the literate comment mode (latex style), and just ran into a problem that seems like it ought to have a simple solution, which is that it seems that haskell requires you to define all the variations of a function sequentially, which is raining on my literate programming parade. Here is what I'd like to do: \begin{code} data D = A String | B String instance Show D where show = showD instance Read D where readsPrec _ = readsD readD s = (readsA s) ++ (readsB s) \end{code} A is formatted like ``A string''. \begin{code} showD (A s) = "A " ++ s readsA s = [(A thestr, r) | ("A", x) <- mylex s, (thestr, r) <- mylex x] \end{code} B is formatted like ``B string''. \begin{code} showD (B s) = "B " ++ s readsB s = [(B thestr, r) | ("B", x) <- mylex s, (thestr, r) <- mylex x] \end{code} The problem I have is that ghc complains because I've split up the definition of showD with readsA defined in between. This surprised me, since it seemed that the code should still be unambiguous. Is there some nice way around this, or do I have to define a separate function for each constructor, and then have a list in one place (as I do with the readsD, in that case because pattern matching won't give me what I want), like: showD (A s) = showA (A s) showD (B s) = showB (B s) Of course, in my actual example, there are more than two constructors, and the parsing is considerably more complex, which is why I'd like to put the analagous showing and parsing right next to eachother along with a description of what the formatting is intended to be. -- David Roundy http://civet.berkeley.edu/droundy/ From franka@cs.uu.nl Sat Sep 21 13:55:24 2002 From: franka@cs.uu.nl (Frank Atanassow) Date: Sat, 21 Sep 2002 14:55:24 +0200 Subject: Show the components of the sum In-Reply-To: <20020921112937.GA9057@jdj5.mit.edu> References: <20020921112937.GA9057@jdj5.mit.edu> Message-ID: <20020921125524.GA8728@cs.uu.nl> David Roundy wrote (on 21-09-02 07:30 -0400): > Here is what I'd like to do: > > \begin{code} > data D = A String | B String > instance Show D where > show = showD > instance Read D where > readsPrec _ = readsD > readD s = (readsA s) ++ (readsB s) > \end{code} > > A is formatted like ``A string''. > \begin{code} > showD (A s) = "A " ++ s > readsA s = [(A thestr, r) | ("A", x) <- mylex s, > (thestr, r) <- mylex x] > \end{code} .. [ and similarly for B ] ... > > The problem I have is that ghc complains because I've split up the > definition of showD with readsA defined in between. This surprised me, > since it seemed that the code should still be unambiguous. > > Is there some nice way around this, There's no way to intersperse clauses of top-level declarations, no. > or do I have to define a separate > function for each constructor, and then have a list in one place (as I do > with the readsD, in that case because pattern matching won't give me what I > want), like: > > showD (A s) = showA (A s) > showD (B s) = showB (B s) Almost. But then showA and showB are partial. It's better to do this: showA s = "A " ++ s and similarly for B, and then: data D = A String | B String instance Show D where show (A s) = showA s show (B s) = showB s instance Read D where readsPrec _ = readsD readD s = (readsA s) ++ (readsB s) What you are doing here basically is just assigning names to the branches of a case-expression: h sum = case sum of Left x -> ... x ... Right y -> ... y ... <= h sum = case sum of Left x -> (\x' -> ... x' ...) x Right y -> (\y' -> ... y' ...) y <= h sum = let f x' = ... x' ... g y' = ... y' ... in case sum of Left x -> f x Right y -> g y <= f x' = ... x' ... g y' = ... y' ... h (Left x) = f x h (Right y) = g y -- Frank From roconnor@Math.Berkeley.EDU Sat Sep 21 20:56:13 2002 From: roconnor@Math.Berkeley.EDU (Russell O'Connor) Date: Sat, 21 Sep 2002 12:56:13 -0700 (PDT) Subject: Monad Maybe? Message-ID: -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 [To: haskell-cafe@haskell.org] Is there a nicer way of writing the following sort of code? case (number g) of Just n -> Just (show n) Nothing -> case (fraction g) of Just n -> Just (show n) Nothing -> case (nimber g) of Just n -> Just ("*"++(show n)) Nothing -> Nothing - -- Russell O'Connor roconnor@math.berkeley.edu ``Any time you skip a commercial [...] you're actually stealing the programming'' -- Jamie Kellner, CEO of TBS -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.6 (SunOS) Comment: For info see http://www.gnupg.org iD8DBQE9jM7juZUa0PWVyWQRAjmlAJ9+YDXUEXEhLTtb2huBZKskJ9JvegCgjPb2 iGb/vYYLK7I+UdfijtEePyQ= =6UZh -----END PGP SIGNATURE----- From dpt@math.harvard.edu Sat Sep 21 23:42:12 2002 From: dpt@math.harvard.edu (Dylan Thurston) Date: Sat, 21 Sep 2002 18:42:12 -0400 Subject: Monad Maybe? In-Reply-To: References: Message-ID: <20020921224212.GB19418@lotus.bostoncoop.net> --EuxKj2iCbKjpUGkD Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sat, Sep 21, 2002 at 12:56:13PM -0700, Russell O'Connor wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 >=20 > [To: haskell-cafe@haskell.org] >=20 > Is there a nicer way of writing the following sort of code? >=20 > case (number g) of > Just n -> Just (show n) > Nothing -> > case (fraction g) of > Just n -> Just (show n) > Nothing -> > case (nimber g) of > Just n -> Just ("*"++(show n)) > Nothing -> Nothing You could write (using GHC's pattern guards): show g | Just n =3D number g =3D Just (show n) | Just n =3D fraction g =3D Just (show n) | Just n =3D nimber g =3D Just ("*"++show n) | Nothing =3D Nothing Do I detect a program for analyzing combinatorial games being written? --Dylan --EuxKj2iCbKjpUGkD Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.7 (GNU/Linux) iD8DBQE9jPXEVeybfhaa3tcRArsPAJ9LSm/YUfL4ohVMMeXYRI7Zkhup6gCdGu2n y5HgyZSr1X6BW6G76uJZNTw= =5bPk -----END PGP SIGNATURE----- --EuxKj2iCbKjpUGkD-- From pixel@mandrakesoft.com Sat Sep 21 23:40:46 2002 From: pixel@mandrakesoft.com (Pixel) Date: 22 Sep 2002 00:40:46 +0200 Subject: Monad Maybe? In-Reply-To: References: Message-ID: "Russell O'Connor" writes: > [To: haskell-cafe@haskell.org] > > Is there a nicer way of writing the following sort of code? > > case (number g) of > Just n -> Just (show n) > Nothing -> > case (fraction g) of > Just n -> Just (show n) > Nothing -> > case (nimber g) of > Just n -> Just ("*"++(show n)) > Nothing -> Nothing what about? listToMaybe $ mapMaybe (\ (f, format) -> fmap format (f g)) l where l = [ (number, show), (fraction, show), (nimber, (\ n -> "*" ++ show n)) ] or: if_just (number g) show $ if_just (fraction g) show $ if_just (nimber g) (\ n -> "*" ++ show n) Nothing using: if_just (Just e) f _ = Just(f e) if_just Nothing _ f = f From ken@digitas.harvard.edu Sat Sep 21 23:37:53 2002 From: ken@digitas.harvard.edu (Ken Shan) Date: Sat, 21 Sep 2002 18:37:53 -0400 Subject: Monad Maybe? In-Reply-To: References: Message-ID: <20020921223753.GA9857@proper.eecs.harvard.edu> --45Z9DzgjV8m4Oswq Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2002-09-21T12:56:13-0700, Russell O'Connor wrote: > case (number g) of > Just n -> Just (show n) > Nothing -> > case (fraction g) of > Just n -> Just (show n) > Nothing -> > case (nimber g) of > Just n -> Just ("*"++(show n)) > Nothing -> Nothing How about something like: msum [ liftM show (number g) , liftM show (fraction g) , liftM (("*"++).show) (nimber g) ] --=20 Edit this signature at http://www.digitas.harvard.edu/cgi-bin/ken/sig So the choice which Lomborg presents us with, of whether to save a drowning Tuvaluan (climate change) or a dying Somalian (water and sanitation) is not= =20 a choice at all -- in fact we need to do both, and not least because one is unlikely to be successful without the other. http://www.anti-lomborg.com/ --45Z9DzgjV8m4Oswq Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.7 (GNU/Linux) iD8DBQE9jPTAzjAc4f+uuBURAurxAKD8SSuUzXx2D3ZsLkYb9ZPY+mZgkgCfUhc0 hVfK4vjO/jQfvgXwyqSvG+o= =MHO1 -----END PGP SIGNATURE----- --45Z9DzgjV8m4Oswq-- From hdaume@ISI.EDU Sun Sep 22 00:54:22 2002 From: hdaume@ISI.EDU (Hal Daume III) Date: Sat, 21 Sep 2002 16:54:22 -0700 (PDT) Subject: Monad Maybe? In-Reply-To: <20020921224212.GB19418@lotus.bostoncoop.net> Message-ID: > show g | Just n = number g = Just (show n) > | Just n = fraction g = Just (show n) > | Just n = nimber g = Just ("*"++show n) > | Nothing = Nothing These should be "Just n <- number g", not "=" - Hal From ajb@spamcop.net Sun Sep 22 04:30:43 2002 From: ajb@spamcop.net (Andrew J Bromage) Date: Sun, 22 Sep 2002 13:30:43 +1000 Subject: Monad Maybe? In-Reply-To: References: Message-ID: <20020922033043.GA7175@smtp.alicorna.com> G'day all. On Sat, Sep 21, 2002 at 12:56:13PM -0700, Russell O'Connor wrote: > case (number g) of > Just n -> Just (show n) > Nothing -> > case (fraction g) of > Just n -> Just (show n) > Nothing -> > case (nimber g) of > Just n -> Just ("*"++(show n)) > Nothing -> Nothing This isn't exactly the most beautiful way of doing it, but... (number g >>= return . show) `mplus` (fraction g >>= return . show) `mplus` (nimber g >>= return . ('*':) . show) Cheers, Andrew Bromage From droundy@jdj5.mit.edu Mon Sep 23 15:06:14 2002 From: droundy@jdj5.mit.edu (David Roundy) Date: Mon, 23 Sep 2002 10:06:14 -0400 Subject: Show the components of the sum In-Reply-To: <20020921125524.GA8728@cs.uu.nl> References: <20020921112937.GA9057@jdj5.mit.edu> <20020921125524.GA8728@cs.uu.nl> Message-ID: <20020923140613.GE1500@jdj5.mit.edu> On Sat, Sep 21, 2002 at 02:55:24PM +0200, Frank Atanassow wrote: > > Almost. But then showA and showB are partial. It's better to do this: > > showA s = "A " ++ s > > and similarly for B, and then: > > data D = A String | B String > instance Show D where > show (A s) = showA s > show (B s) = showB s > instance Read D where > readsPrec _ = readsD > readD s = (readsA s) ++ (readsB s) Thank you for this advice! This solved my quandry quite cleanly. -- David Roundy http://civet.berkeley.edu/droundy/ From hdaume@ISI.EDU Mon Sep 23 22:57:45 2002 From: hdaume@ISI.EDU (Hal Daume III) Date: Mon, 23 Sep 2002 14:57:45 -0700 (PDT) Subject: Monad Maybe? In-Reply-To: <20020922033043.GA7175@smtp.alicorna.com> Message-ID: I know this has been written about way too much, but I was wondering what people thought about using 'liftM f' as opposed to '>>= return . f'. I would probably have written Andrew's code using liftM, but I don't know if one is necessarily better than the other. Does anyone have strong thoughts on this? -- Hal Daume III "Computer science is no more about computers | hdaume@isi.edu than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume On Sun, 22 Sep 2002, Andrew J Bromage wrote: > G'day all. > > On Sat, Sep 21, 2002 at 12:56:13PM -0700, Russell O'Connor wrote: > > > case (number g) of > > Just n -> Just (show n) > > Nothing -> > > case (fraction g) of > > Just n -> Just (show n) > > Nothing -> > > case (nimber g) of > > Just n -> Just ("*"++(show n)) > > Nothing -> Nothing > > This isn't exactly the most beautiful way of doing it, but... > > (number g >>= return . show) `mplus` > (fraction g >>= return . show) `mplus` > (nimber g >>= return . ('*':) . show) > > Cheers, > Andrew Bromage > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > From diatchki@cse.ogi.edu Tue Sep 24 00:30:35 2002 From: diatchki@cse.ogi.edu (Iavor Diatchki) Date: Mon, 23 Sep 2002 16:30:35 -0700 Subject: Monad Maybe? In-Reply-To: ; from hdaume@ISI.EDU on Mon, Sep 23, 2002 at 02:57:45PM -0700 References: <20020922033043.GA7175@smtp.alicorna.com> Message-ID: <20020923163035.C9409@cse.ogi.edu> hi, i personally think that one should use fmap instead. it tells you exactly how much structure you need. having said that it is sometimes annoying to get the extra Functor constraint (alas Functor is not a super class of Moand)... so my preference is: 1. fmap 2. liftM 3. bind with return bye iavor On Mon, Sep 23, 2002 at 02:57:45PM -0700, Hal Daume III wrote: > I know this has been written about way too much, but I was wondering what > people thought about using 'liftM f' as opposed to '>>= return . f'. I > would probably have written Andrew's code using liftM, but I don't know if > one is necessarily better than the other. Does anyone have strong > thoughts on this? > > -- > Hal Daume III > > "Computer science is no more about computers | hdaume@isi.edu > than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume > > On Sun, 22 Sep 2002, Andrew J Bromage wrote: > > > G'day all. > > > > On Sat, Sep 21, 2002 at 12:56:13PM -0700, Russell O'Connor wrote: > > > > > case (number g) of > > > Just n -> Just (show n) > > > Nothing -> > > > case (fraction g) of > > > Just n -> Just (show n) > > > Nothing -> > > > case (nimber g) of > > > Just n -> Just ("*"++(show n)) > > > Nothing -> Nothing > > > > This isn't exactly the most beautiful way of doing it, but... > > > > (number g >>= return . show) `mplus` > > (fraction g >>= return . show) `mplus` > > (nimber g >>= return . ('*':) . show) > > > > Cheers, > > Andrew Bromage > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe@haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe -- ---------------------------------------+---------------------------------------- Iavor S. Diatchki | email: diatchki@cse.ogi.edu Dept. of Computer Science | web: http://www.cse.ogi.edu/~diatchki OGI School of Science and Engineering | work phone: 5037481631 OHSU | home phone: 5036434085 ---------------------------------------+---------------------------------------- From =?KOI8-R?Q?=F6=C2=C1=CE=CF=D7_=F0=C1=D7=C5=CC_=E7=C5=CE=CE=C1=C4?= Tue Sep 24 12:14:28 2002 From: =?KOI8-R?Q?=F6=C2=C1=CE=CF=D7_=F0=C1=D7=C5=CC_=E7=C5=CE=CE=C1=C4?= (=?KOI8-R?Q?=F6=C2=C1=CE=CF=D7_=F0=C1=D7=C5=CC_=E7=C5=CE=CE=C1=C4?=) Date: Tue, 24 Sep 2002 15:14:28 +0400 Subject: Problems with IO Message-ID: <3D904914.9090501@joker.botik.ru> I'm having a problem with writing a function dealing with I/O. Maybe it's just a lack of experience or simple Haskell knowledge because I'm just a beginer. The problem: I want to write a function that converts an IO String into String lala :: IO String -> String Is it possible? If yes, how? -- �� From =?ISO-8859-1?Q?=3F=3F=3F=3F=3F=3F_=3F=3F=3F=3F=3F_=3F=3F=3F=3F=3F?= Tue Sep 24 12:46:49 2002 From: =?ISO-8859-1?Q?=3F=3F=3F=3F=3F=3F_=3F=3F=3F=3F=3F_=3F=3F=3F=3F=3F?= (=?ISO-8859-1?Q?=3F=3F=3F=3F=3F=3F_=3F=3F=3F=3F=3F_=3F=3F=3F=3F=3F?=) Date: Tue, 24 Sep 2002 15:46:49 +0400 Subject: Problems with IO References: Message-ID: <3D9050A7.4070001@joker.botik.ru> Now I understand that it's just a lack of knowledge... Sorry for interrupring... By the way, can you recommend a good manual which I can find on the web? -- Zhbanov Pavel From glynn.clements@virgin.net Tue Sep 24 12:49:33 2002 From: glynn.clements@virgin.net (Glynn Clements) Date: Tue, 24 Sep 2002 12:49:33 +0100 Subject: Problems with IO In-Reply-To: <3D9050A7.4070001@joker.botik.ru> References: <3D9050A7.4070001@joker.botik.ru> Message-ID: <15760.20813.158394.704537@cerise.nosuchdomain.co.uk> Zhbanov Pavel wrote: > Now I understand that it's just a lack of knowledge... Sorry for > interrupring... > > By the way, can you recommend a good manual which I can find on the web? Tutorial: http://www.haskell.org/tutorial/ Reference Manual: http://www.haskell.org/definition/ Further Information: http://www.haskell.org/bookshelf/ -- Glynn Clements From herrmann@fmi.uni-passau.de Tue Sep 24 12:57:28 2002 From: herrmann@fmi.uni-passau.de (Ch. A. Herrmann) Date: Tue, 24 Sep 2002 13:57:28 +0200 Subject: Problems with IO In-Reply-To: <3D9050A7.4070001@joker.botik.ru> References: <3D9050A7.4070001@joker.botik.ru> Message-ID: <15760.21288.977737.108027@debussy.fmi.uni-passau.de> >>>>> "pavel" == pavel writes: pavel> Now I understand that it's just a lack of knowledge... Sorry pavel> for interrupring... pavel> By the way, can you recommend a good manual which I can find pavel> on the web? The best source would be a good book like Simon Thompsons: "Haskell: The Craft of Functional Programming", published by Addison-Wesley. I/O is described in Chapter 18 on page 383 which makes clear that I/O is not the first thing you should try when learning Haskell. Use an interpreter like ghci first and evaluate expressions in interaction with the interpreter. You can also find a tutorial on the web at: http://www.haskell.org/tutorial/ Cheers -- Christoph Herrmann From =?ISO-8859-1?Q?=3F=3F=3F=3F=3F=3F_=3F=3F=3F=3F=3F_=3F=3F=3F=3F=3F?= Tue Sep 24 13:59:07 2002 From: =?ISO-8859-1?Q?=3F=3F=3F=3F=3F=3F_=3F=3F=3F=3F=3F_=3F=3F=3F=3F=3F?= (=?ISO-8859-1?Q?=3F=3F=3F=3F=3F=3F_=3F=3F=3F=3F=3F_=3F=3F=3F=3F=3F?=) Date: Tue, 24 Sep 2002 16:59:07 +0400 Subject: Problems with IO References: <3D9050A7.4070001@joker.botik.ru> <15760.21288.977737.108027@debussy.fmi.uni-passau.de> Message-ID: <3D906187.7060109@joker.botik.ru> My task is to write a parser for some language (TSG). I'm using an UU_Parsing library. I wrote that parser even tested it by using some example provided, but I have problems with using my parser. I wrote a function: > test :: [Char] -> IO () > test inp = do res <- parseIO pTSG inp > print res parseIO :: InputState a b => AnaParser a Pair b c -> a b -> IO c is provided by the library, pTSG is my parser and inp is a String that I'm parsing. How can I use that function "test" while using readFile? Is it something like: > test1 file = do inp <- readFile file > test inp Why should I use that "do" thing? What is so "magical" in it? PS: Please, don't say that I'm stupid, I just have problem with understanding IO/Monad part, besides that is just me second week of Haskell... :) PS1: "Haskell: The Craft of Functional Programming" didn't make that part clear to me. That's why I'm writing... -- Pavel Zhbanov From herrmann@fmi.uni-passau.de Tue Sep 24 14:15:05 2002 From: herrmann@fmi.uni-passau.de (Ch. A. Herrmann) Date: Tue, 24 Sep 2002 15:15:05 +0200 Subject: Problems with IO In-Reply-To: <3D906187.7060109@joker.botik.ru> References: <3D9050A7.4070001@joker.botik.ru> <15760.21288.977737.108027@debussy.fmi.uni-passau.de> <3D906187.7060109@joker.botik.ru> Message-ID: <15760.25945.903554.449036@debussy.fmi.uni-passau.de> Hi Pavel, >>>>> "pavel" == pavel writes: pavel> My task is to write a parser for some language (TSG). pavel> ... pavel> Why should I use that "do" thing? What is so "magical" in it? pavel> PS: Please, don't say that I'm stupid, I just have problem pavel> with understanding IO/Monad part, besides that is just me pavel> second week of Haskell... :) I think that your task is not appropriate for a Haskell beginner. You should go to the person who gave you the task and tell him/her that you need much more time to learn Haskell, understand how monads are to be used and, maybe, what type classes are. Otherwise, you cannot guarantee that your program will work the way it is supposed to. Good luck -- Christoph From simonmar@microsoft.com Tue Sep 24 14:24:47 2002 From: simonmar@microsoft.com (Simon Marlow) Date: Tue, 24 Sep 2002 14:24:47 +0100 Subject: Monad Maybe? Message-ID: <9584A4A864BD8548932F2F88EB30D1C60A69EA83@TVP-MSG-01.europe.corp.microsoft.com> > I know this has been written about way too much, but I was=20 > wondering what > people thought about using 'liftM f' as opposed to '>>=3D=20 > return . f'. I > would probably have written Andrew's code using liftM, but I=20 > don't know if > one is necessarily better than the other. Does anyone have strong > thoughts on this? so, using liftM: (number g >>=3D return . show) becomes (liftM show (number g)) or (show `liftM` number g) but it's important not to get too carried away with abstractions - this example requires a bit of a trawl around the library documentation for someone not familiar with liftM. Personally, unless I was writing fragments like this a lot, I'd just write it as (do r <- number g; return (show r)) Each to his own I suppose. Cheers, Simon From alastair@reid-consulting-uk.ltd.uk Tue Sep 24 17:28:18 2002 From: alastair@reid-consulting-uk.ltd.uk (Alastair Reid) Date: 24 Sep 2002 17:28:18 +0100 Subject: Monad Maybe? In-Reply-To: References: Message-ID: Hal Daume writes: > I know this has been written about way too much, but I was wondering > what people thought about using 'liftM f' as opposed to '>>= return . f'. > I would probably have written Andrew's code using liftM, but > I don't know if one is necessarily better than the other. Does > anyone have strong thoughts on this? I tend to use liftM only as part of a pattern of lifting a family of non-monadic functions up to the monadic level in code like this: instance (Monad m, Num a) => Num (m a) where (+) = liftM2 (+) (-) = liftM2 (-) negate = liftM1 negate ... instance (Monad m, Integral a) => Integral (m a) where ... If it doesn't feel like lifting and/or it isn't part of a pattern like the above, I tend not to use it. A From gkosmidis@epsilon7.gr Wed Sep 25 14:14:06 2002 From: gkosmidis@epsilon7.gr (=?iso-8859-1?Q?G=3F=3F=3F=3F=3F=3F_=3F=3Fs=B5=3Fd=3F=3F?=) Date: Wed, 25 Sep 2002 16:14:06 +0300 Subject: new to haskell-not working for some reason References: <20020918160103.9F2AC4223C1@www.haskell.org><001301c25fac$fbdddcb0$6000000a@dbserver><20020919134915.5c7190f4.Malcolm.Wallace@cs.york.ac.uk><009901c25fe9$86b08810$6000000a@dbserver> <20020919153326.42949bb9.Malcolm.Wallace@cs.york.ac.uk> Message-ID: <001801c26495$6e40cb40$6000000a@dbserver> I am new to haskell. I am trying to do some "excersise" but i can't make anything work :( This is my code.I replaced spaces with underscores ( _ ) Thanks for any suggestions or correctrions import IO import System import List import Maybe import Char import Numeric type Name=String type Room=Int type Dr=String type PatientTup=(Name,(Room,Dr)) type PatientList=[PatientTup] main=do userText<-getText ---------------------------------------------------------------------------- ------- ________getText::IO String ________getText=do nc<-getText _______________________return (:nc) ---------------------------------------------------------------------------- ------- ________PatientList::[(String,(Int,String))] ________PatientList=[("Robson, Brian",(2,"MJH")), _____________________("Hitchin, Linda",(1,"ILR")), _____________________("Reeve, Paul", (2,"ILR"))] ---------------------------------------------------------------------------- ------- ________getWards::Int ________getWards PatientList=[Room | (Name,(Room,Dr)) <- PatientList, Room==getText] _________________do putSpc (length Room) _________________return(RoomLength) ---------------------------------------------------------------------------- ------- ________printFreq::WordList->IO() ________printFreq wl=do sequence (map putWards wl) _________________________________where ______________________________________putWards::(getWards)->IO() ______________________________________putWards(w)=do putStr w _____________________________________________________putChar '\n' _____________________________________________________return(w) From hdaume@ISI.EDU Wed Sep 25 15:44:33 2002 From: hdaume@ISI.EDU (Hal Daume III) Date: Wed, 25 Sep 2002 07:44:33 -0700 (PDT) Subject: new to haskell-not working for some reason In-Reply-To: <001801c26495$6e40cb40$6000000a@dbserver> Message-ID: Among other things, please make sure your layout lines up. Also, you cannot have the definition of getText at the same indentation of "userText<-getText" otherwise your compiler will think this is part of the do statement (I believe): > main=do userText<-getText > ---------------------------------------------------------------------------- > ------- > ________getText::IO String > ________getText=do nc<-getText > _______________________return (:nc) these need to be lined up > _________________do putSpc (length Room) > _________________return(RoomLength) It would help if you also posted the error messaage the compiler gave you and the line number and (perhaps) a shorter version of the program. - Hal From carctol@yahoo.com Wed Sep 25 22:13:09 2002 From: carctol@yahoo.com (carctol@yahoo.com) Date: Wed, 25 Sep 2002 17:13:09 -0400 (EDT) Subject: Kanser tedavisi Message-ID: <20020925211309.19D24422078@www.haskell.org> charset="US-ASCII"; charset="US-ASCII"; charset="US-ASCII"; charset="US-ASCII" Reply-To: carctol@yahoo.com Date: Thu, 26 Sep 2002 00:12:08 +0300 X-Priority: 3 X-Library: Indy 9.00.10 X-Mailer: Foxmail Kemoterapinin yan etkileri nedeniyle yorgun ve bitkin d�sm�s bir yakininiz mi var? Yanitiniz evetse vakit kaybetmeyin ve CARCTOL'u denemesini saglayin. Genelde ancak klasik tedavinin ise yaramadiginin anlasilmasi, insanlari baska se�enekler aramaya itmektedir, ancak o durumda maalesef yapacak fazla birsey kalmamaktadir. Ayni hatanin yapilmasina izin vermeyin ve hi�bir yan etkisi olmayan, Himalaya Dagi bitkilerinden �retilen Carctol'u denemesini saglayin. CARCTOL, birka� bin yillik, alternatif Hint Tibbinin (Ayuverda'nin) insanliga sundugu bir umut isigidir. �nceleri v�cudu takviye edici tonik olarak kullanilan bu �r�n simdi yeni form�l�yle kansere karsi etkili bir ila�tir L�tfen asagidaki siteye ugrayin ve Carctol'u yakindan taniyin. http://www.kanser-tedavisi.com esenlikler dileriz.. Listeden adinizin silinmesini istiyorsaniz a_cengiz2002@yahoo.com a bos e posta yollayin. Tesekk�rler From liyang@nerv.cx Thu Sep 26 00:06:36 2002 From: liyang@nerv.cx (Liyang Hu) Date: Thu, 26 Sep 2002 00:06:36 +0100 Subject: Dealing with configuration data Message-ID: <20020925230636.GA30622@sakura.local.nerv.cx> --mYCpIKhGyMATD0i+ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Evening, I'm trying to write a utility that reads in some user preferences from a pre-determined file, does some work, and exits. Sounds simple enough. The problem I'm having is with the preferences: How do I make it available throughout the entire program? (FWIW, most of the work is effectively done inside the IO monad.) I could explicitly pass the record around everywhere, but that seems a trifle inelegant. My current solution is to use a global ('scuse my terminology, I'm not sure that's the right word to use here) variable of type IORef Config obtained through unsafePerformIO. It works, but strikes me as a rather barbaric solution to a seemingly tame enough problem... Intuition tells me I should be able to `embed', if you will, the config record somehow within or alongside the IO state, and retrieve it at will. (Is this what MonadState is for?) However it also tells me that this will /probably/ involve lots of needless lifting and rewriting of the existing code, which makes it even less enticing than passing everything around explicitly. Any opinions or suggestions? Cheers, /Liyang --=20 =2E--{ Liyang HU }--{ http://nerv.cx/ }--{ Caius@Cam }--{ ICQ: 39391385 }--. | :: zettai unmei mokusiroku :::: absolute destined apocalypse ::::::::: | --mYCpIKhGyMATD0i+ Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.6 (GNU/Linux) Comment: moo! (ID: 7B632CB8) iEYEARECAAYFAj2SQXwACgkQ1QR4EHtjLLjwHwCg7cZF+od6Ow+2xmBDVdN5W5K7 HaUAnjeTfReSxXfw02eat0sF0hgQStAi =Oxsh -----END PGP SIGNATURE----- --mYCpIKhGyMATD0i+-- From hdaume@ISI.EDU Thu Sep 26 00:06:29 2002 From: hdaume@ISI.EDU (Hal Daume III) Date: Wed, 25 Sep 2002 16:06:29 -0700 (PDT) Subject: Dealing with configuration data In-Reply-To: <20020925230636.GA30622@sakura.local.nerv.cx> Message-ID: AFAIK, the global variable (so-called), passing around, and lifting the IO monad are your only options. I almost always use the global variable method since I know that in this case the unsafePerformIO is actually safe, since writing to the variable will always occur before the call to upIO and that it will only be written once. I don't feel bad about doing this because GHC does this itself for its own configuration :). -- Hal Daume III "Computer science is no more about computers | hdaume@isi.edu than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume On Thu, 26 Sep 2002, Liyang Hu wrote: > Evening, > > I'm trying to write a utility that reads in some user preferences from > a pre-determined file, does some work, and exits. Sounds simple enough. > > The problem I'm having is with the preferences: How do I make it > available throughout the entire program? (FWIW, most of the work is > effectively done inside the IO monad.) I could explicitly pass the > record around everywhere, but that seems a trifle inelegant. > > My current solution is to use a global ('scuse my terminology, I'm not > sure that's the right word to use here) variable of type IORef Config > obtained through unsafePerformIO. It works, but strikes me as a rather > barbaric solution to a seemingly tame enough problem... > > Intuition tells me I should be able to `embed', if you will, the config > record somehow within or alongside the IO state, and retrieve it at > will. (Is this what MonadState is for?) However it also tells me that > this will /probably/ involve lots of needless lifting and rewriting of > the existing code, which makes it even less enticing than passing > everything around explicitly. > > Any opinions or suggestions? > > Cheers, > /Liyang > -- > .--{ Liyang HU }--{ http://nerv.cx/ }--{ Caius@Cam }--{ ICQ: 39391385 }--. > | :: zettai unmei mokusiroku :::: absolute destined apocalypse ::::::::: | > From hdaume@ISI.EDU Thu Sep 26 00:09:24 2002 From: hdaume@ISI.EDU (Hal Daume III) Date: Wed, 25 Sep 2002 16:09:24 -0700 (PDT) Subject: Dealing with configuration data In-Reply-To: Message-ID: Sorry, I should also mention implicit parameters, if you're willing to use that extension. I don't like them, though, and my impression from SPJ is that it's very unclear whether they will get into Haskell 2 or not... -- Hal Daume III "Computer science is no more about computers | hdaume@isi.edu than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume On Wed, 25 Sep 2002, Hal Daume III wrote: > AFAIK, the global variable (so-called), passing around, and lifting the IO > monad are your only options. I almost always use the global variable > method since I know that in this case the unsafePerformIO is actually > safe, since writing to the variable will always occur before the call to > upIO and that it will only be written once. I don't feel bad about doing > this because GHC does this itself for its own configuration :). > > -- > Hal Daume III > > "Computer science is no more about computers | hdaume@isi.edu > than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume > > On Thu, 26 Sep 2002, Liyang Hu wrote: > > > Evening, > > > > I'm trying to write a utility that reads in some user preferences from > > a pre-determined file, does some work, and exits. Sounds simple enough. > > > > The problem I'm having is with the preferences: How do I make it > > available throughout the entire program? (FWIW, most of the work is > > effectively done inside the IO monad.) I could explicitly pass the > > record around everywhere, but that seems a trifle inelegant. > > > > My current solution is to use a global ('scuse my terminology, I'm not > > sure that's the right word to use here) variable of type IORef Config > > obtained through unsafePerformIO. It works, but strikes me as a rather > > barbaric solution to a seemingly tame enough problem... > > > > Intuition tells me I should be able to `embed', if you will, the config > > record somehow within or alongside the IO state, and retrieve it at > > will. (Is this what MonadState is for?) However it also tells me that > > this will /probably/ involve lots of needless lifting and rewriting of > > the existing code, which makes it even less enticing than passing > > everything around explicitly. > > > > Any opinions or suggestions? > > > > Cheers, > > /Liyang > > -- > > .--{ Liyang HU }--{ http://nerv.cx/ }--{ Caius@Cam }--{ ICQ: 39391385 }--. > > | :: zettai unmei mokusiroku :::: absolute destined apocalypse ::::::::: | > > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > From nick.name@inwind.it Thu Sep 26 00:33:14 2002 From: nick.name@inwind.it (Nick Name) Date: Thu, 26 Sep 2002 01:33:14 +0200 Subject: Dealing with configuration data In-Reply-To: References: <20020925230636.GA30622@sakura.local.nerv.cx> Message-ID: <20020926013314.5da489b7.nick.name@inwind.it> On Wed, 25 Sep 2002 16:06:29 -0700 (PDT) Hal Daume III wrote: > I don't feel bad about doing > this because GHC does this itself for its own configuration :). I am going to show you that using unsafePerformIO where there really are side effects leads to unpredictable results, and is generally wrong in a lazy language. Don't hate me for this :) Consider this example (supposing that a Config is represented by an Int): storeConfig :: Int -> () readConfig :: Int They both are obtained through the use of "unsafePerformIO". Now, say I got this code: (storeConfig 0,storeConfig 1,readConfig,storeConfig 0,readConfig) What is this 5-uple supposed to evaluate to? First of all, this depends on order of evaluation. We can't say that all the elements of the tuple will be evaluated, so we can't tell if the fifth readConfig will evaluate to 0 or 1 (if the third storeConfig is never evaluated, readConfig will evaluate to 0, else to 1) This is one of the causes of the use of monads: ensuring correct order of evaluation. Second, suppose we were able to force order of evaluation (which shouldn't be allowed, in a lazy language). We still can't say what the last "readConfig" would evaluate to, since we don't know if the compiler is substituting equals for equals (I am expecting a lazy functional language to do this). If the compiler does, the last readConfig is equal to the first (in fact, by the use of unsafePerformIO, you have told the compiler that both the functions storeConfig and readConfig are pure, which is not true) and will evaluate to 1, else it will evaluate to 0. And, besides, the compiler should also substitute the second "storeConfig 0" with the result of the first occurrence, so it would not evaluate the second "storeConfig" at all. This is another example of the need for monads: allowing program transformations, first of all substituting equals for equals. This is why (even if, by enough knoweledge of the implementation, we could), by only relying on the semantics of a lazy language, we can not have functions with side effects. If it wasn't so, they would not have invented monads, believe me. I apologize, as always, for my terrible english, and hope I have been clear. Vincenzo Ciancia From jadrian@mat.uc.pt Thu Sep 26 00:31:00 2002 From: jadrian@mat.uc.pt (Jorge Adriano) Date: Thu, 26 Sep 2002 00:31:00 +0100 Subject: Dealing with configuration data In-Reply-To: <20020925230636.GA30622@sakura.local.nerv.cx> References: <20020925230636.GA30622@sakura.local.nerv.cx> Message-ID: <200209260030.12960.jadrian@mat.uc.pt> > Evening, > > I'm trying to write a utility that reads in some user preferences from > a pre-determined file, does some work, and exits. Sounds simple enough. > > The problem I'm having is with the preferences: How do I make it > available throughout the entire program? (FWIW, most of the work is > effectively done inside the IO monad.) I could explicitly pass the > record around everywhere, but that seems a trifle inelegant. > > My current solution is to use a global ('scuse my terminology, I'm not > sure that's the right word to use here) variable of type IORef Config > obtained through unsafePerformIO. It works, but strikes me as a rather > barbaric solution to a seemingly tame enough problem... > > Intuition tells me I should be able to `embed', if you will, the config > record somehow within or alongside the IO state, and retrieve it at > will. (Is this what MonadState is for?) However it also tells me that > this will /probably/ involve lots of needless lifting and rewriting of > the existing code, which makes it even less enticing than passing > everything around explicitly. This is how I usually do it: http://www.mail-archive.com/haskell@haskell.org/msg10565.html (ignore the last part of the post...) J.A. From hdaume@ISI.EDU Thu Sep 26 00:34:02 2002 From: hdaume@ISI.EDU (Hal Daume III) Date: Wed, 25 Sep 2002 16:34:02 -0700 (PDT) Subject: Dealing with configuration data In-Reply-To: <20020926013314.5da489b7.nick.name@inwind.it> Message-ID: I don't mean to troll, but this isn't what I meant. Suppose we have: data Configuration = ... -- config data globalConfig :: IORef Configuration globalConfig = unsafePerformIO (newIORef undefined) Now, we define an unsafe function to read the configuration: getConfig :: Configuration getConfig = unsafePerformIO $ readIORef globalConfig Okay, this is "bad" but I claim it's okay, iff it is used as in: main = do ...read configuration from file...no calls to getConfig... writeIORef globalConfig configuration doStuff return () now, we have doStuff :: IO a. doStuff is allowed (even in its pure methods) to use getConfig. I claim that this is safe. I could be wrong; this is only a hand-waiving argument. Why? The first reference in the program to globalConfig is through a writeIORef. This means that at this point globalConfig gets evaluated and thus a ref is created. Immediately we put a value in it. Now, when doStuff runs, since it is an action run *after* the call to writeIORef, provided that it doesn't also write to 'globalConfig' (which I mentioned in my original message), any call to getConfig is deterministic. I could be wrong...please correct me if I am. -- Hal Daume III "Computer science is no more about computers | hdaume@isi.edu than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume On Thu, 26 Sep 2002, Nick Name wrote: > On Wed, 25 Sep 2002 16:06:29 -0700 (PDT) > Hal Daume III wrote: > > > I don't feel bad about doing > > this because GHC does this itself for its own configuration :). > > I am going to show you that using unsafePerformIO where there really are > side effects leads to unpredictable results, and is generally wrong in a > lazy language. Don't hate me for this :) > > Consider this example (supposing that a Config is represented by an > Int): > > storeConfig :: Int -> () > readConfig :: Int > > They both are obtained through the use of "unsafePerformIO". > > Now, say I got this code: > > (storeConfig 0,storeConfig 1,readConfig,storeConfig 0,readConfig) > > What is this 5-uple supposed to evaluate to? > > First of all, this depends on order of evaluation. We can't say that all > the elements of the tuple will be evaluated, so we can't tell if the > fifth readConfig will evaluate to 0 or 1 (if the third storeConfig is > never evaluated, readConfig will evaluate to 0, else to 1) This is one > of the causes of the use of monads: ensuring correct order of > evaluation. > > Second, suppose we were able to force order of evaluation (which > shouldn't be allowed, in a lazy language). We still can't say what the > last "readConfig" would evaluate to, since we don't know if the compiler > is substituting equals for equals (I am expecting a lazy functional > language to do this). > > If the compiler does, the last readConfig is equal to the first (in > fact, by the use of unsafePerformIO, you have told the compiler that > both the functions storeConfig and readConfig are pure, which is not > true) and will evaluate to 1, else it will evaluate to 0. And, besides, > the compiler should also substitute the second "storeConfig 0" with the > result of the first occurrence, so it would not evaluate the second > "storeConfig" at all. > > This is another example of the need for monads: allowing program > transformations, first of all substituting equals for equals. > > This is why (even if, by enough knoweledge of the implementation, we > could), by only relying on the semantics of a lazy language, we can not > have functions with side effects. > > If it wasn't so, they would not have invented monads, believe me. > > I apologize, as always, for my terrible english, and hope I have been > clear. > > Vincenzo Ciancia > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > From sales@smokersassociation.co.uk Wed Sep 25 23:36:43 2002 From: sales@smokersassociation.co.uk (Sales Department) Date: Thu, 26 Sep 2002 00:36:43 +0200 Subject: Low Price Fags Message-ID: <20020926003656.B0F554223AC@www.haskell.org> Dear Sir or Madam In the past you have requested information on discounted products. We hope that you find this of interest. If you are not a smoker, and find this email offensive, we sincerely apologise! We will be only too happy to take you off our mailing list. If you are a smoker, however, and are fed up with paying high prices for your cigarettes and tobacco, take a look at what we have to offer by clicking on this link. http://www.smokersassociation.co.uk/?S=15&ID=2 We can send you, legally, by registered air mail, direct to your door, 4 cartons of cigarettes or 40 pouches of rolling tobacco (all brands are available) from only 170 Euros - about 105 pounds - fully inclusive of postage and packing. Why pay more? To remove yourself from our mailing list, please click below mailto:unsubscribe@smokersassociation.co.uk Yours faithfully. Smokers Association http://www.smokersassociation.co.uk/?S=15&ID=2 xay5402731y From ajb@spamcop.net Thu Sep 26 02:09:18 2002 From: ajb@spamcop.net (Andrew J Bromage) Date: Thu, 26 Sep 2002 11:09:18 +1000 Subject: Dealing with configuration data In-Reply-To: <20020925230636.GA30622@sakura.local.nerv.cx> References: <20020925230636.GA30622@sakura.local.nerv.cx> Message-ID: <20020926010918.GA16066@smtp.alicorna.com> G'day all. On Thu, Sep 26, 2002 at 12:06:36AM +0100, Liyang Hu wrote: > The problem I'm having is with the preferences: How do I make it > available throughout the entire program? (FWIW, most of the work is > effectively done inside the IO monad.) I could explicitly pass the > record around everywhere, but that seems a trifle inelegant. > > My current solution is to use a global ('scuse my terminology, I'm not > sure that's the right word to use here) variable of type IORef Config > obtained through unsafePerformIO. It works, but strikes me as a rather > barbaric solution to a seemingly tame enough problem... One solution is to do precisely as you suggested, using a state monad to wrap the IORef. For example: import Control.Monad.Reader import Data.IORef type MyIO a = ReaderT (IORef Config) IO a main = do config <- readConfigurationStuff configref <- newIORef config runReaderT configref main' getConfig :: MyIO Config getConfig = do configref <- ask liftIO (readIORef configref) -- Same as above, but you can supply a projection function. getsConfig :: (Config -> a) -> MyIO a getsConfig f = do config <- getConfig return (f config) -- ...and this is where the code REALLY starts. main' :: MyIO () main' = do config <- getConfig liftIO (putStrLn (show config)) -- etc You can wrap whole slabs of existing code in liftIO if it uses IO but does not need to read the configuration. There's also a much uglier solution which I occasionally use if I need an "ad hoc" global variable. Rather than using IORefs, I use Strings as keys. The code is here: http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/hfl/hfl/ioext/ Example of use: import IOGlobal main :: IO () main = do writeIOGlobalM "foo" "Foo data" writeIOGlobalM "bar" ("Bar", ["data"]) foo <- readIOGlobalM "foo" putStrLn foo bar <- readIOGlobalM "bar" putStrLn (show (bar :: (String, [String]))) Cheers, Andrew Bromage From koen@cs.chalmers.se Thu Sep 26 07:47:56 2002 From: koen@cs.chalmers.se (Koen Claessen) Date: Thu, 26 Sep 2002 08:47:56 +0200 (MET DST) Subject: Dealing with configuration data In-Reply-To: Message-ID: Hal Daume III suggested: | data Configuration = ... -- config data | | globalConfig :: IORef Configuration | globalConfig = unsafePerformIO (newIORef undefined) : | getConfig :: Configuration | getConfig = unsafePerformIO $ readIORef globalConfig : | main = do | ...read configuration from file...no calls to getConfig... | writeIORef globalConfig configuration | doStuff | return () In this case, there is no need to use unsafePerformIO more than once, nor does one need IORefs. Here is how: data Configuration = ... -- config data getConfig :: Configuration getConfig = unsafePerformIO $ do ...read configuration from file... return configuration main = do doStuff We know getConfig will only be evaluated once (because of sharing) (*) Don't use the dirty stuff when you do not have to! :-) I think GHC even supports a function getArgs which is not in the IO monad since the arguments to a program do not change during a program. If getConfig only depends on the arguments, no unsafePerformIO is necessary at all. Gofer, and even early versions of Hugs, had a function openFile :: FilePath -> String. Thge rationale was (I guess) that the contents of a file would not change during the evaluation of a Gofer program. Regards, /Koen. (*) Actually, a Haskell compiler is free to inline these kind of expressions, so really one has to give a NOINLINE pragma to the compiler as well. -- Koen Claessen http://www.cs.chalmers.se/~koen Chalmers University, Gothenburg, Sweden. From koen@cs.chalmers.se Thu Sep 26 08:07:57 2002 From: koen@cs.chalmers.se (Koen Claessen) Date: Thu, 26 Sep 2002 09:07:57 +0200 (MET DST) Subject: Pure File Reading (was: Dealing with configuration data) In-Reply-To: Message-ID: Dear all, At the moment, a discussion on haskell-cafe is going on about how to neatly program the fact that an entire program depends on a number of parameters that are read in once at the beginning of a program. The suggestion that many people came up with was using unsafePerformIO in the beginning to read the file. Here is my version of that: | data Configuration = ... -- config data | | getConfig :: Configuration | getConfig = unsafePerformIO $ | do ...read configuration from file... | return configuration | | main = | do doStuff It is quite disturbing that there is no other easy way to do this than using unsafePerformIO (except for using implicit parameters perhaps, but there are other reasons for not using those). I have been thinking a little bit more about this and here is what I found. Remember the Gofer days, when Gofer had a "function": openFile :: FilePath -> String This was of course a cheap and dirty way of implementing things like the getConfig above, but it is impure. However, one could imagine a functional version of this function: readFileOnce :: FilePath -> Maybe String This function will read the contents of the file (and return Nothing if something went wrong), but it is memoized, so that the second time you use this function you get the same result. So, it is a pure function. (Admittedly, it is somewhat unpredictable, but you will always get the same result for the same arguments.) It is no more strange than GHC's pure version of the getArgs function (I forgot what it was/is called). How about space behavior, you say? Reading a file, and memoizing the result means storing the whole contents of the file in memory! The point is that the use of this function will typically happen at the beginning of a program, when reading the configuration file(s). When all this has happened, the function readFileOnce, and its memo table, will be garabage collected. (Of course there is no guarantee that all calls to readFileOnce will be evaluated at the beginning of a program, and it is not required, but when you do, there are no space problems.) There could of course be pure "-Once" versions of other IO operations. Here is a list of possibilities: - reading a file - getting arguments - getting environment variables - downloading a webpage - ... What do you think? Regards, /Koen. -- Koen Claessen http://www.cs.chalmers.se/~koen Chalmers University, Gothenburg, Sweden. From simonpj@microsoft.com Thu Sep 26 08:37:59 2002 From: simonpj@microsoft.com (Simon Peyton-Jones) Date: Thu, 26 Sep 2002 08:37:59 +0100 Subject: Dealing with configuration data Message-ID: | Sorry, I should also mention implicit parameters, if you're willing to use | that extension. I don't like them, though, and my impression from SPJ is | that it's very unclear whether they will get into Haskell 2 or not... It's *linear* implicit parameters that are a weird beast. Ordinary implicit parameters are quite well behaved. =20 Having said that, there is no Haskell 2 process at the moment... Simon From Yoann.Padioleau@irisa.fr Thu Sep 26 14:09:13 2002 From: Yoann.Padioleau@irisa.fr (Yoann Padioleau) Date: 26 Sep 2002 15:09:13 +0200 Subject: Pure File Reading (was: Dealing with configuration data) In-Reply-To: Koen Claessen's message of "Thu, 26 Sep 2002 09:07:57 +0200 (MET DST)" References: Message-ID: Koen Claessen writes: i find your idea very good. indeed for the library GetOpt, the argument of a program never change so it make sense to make this library without using IO monad, same for argv and for the enviroment. for openFile it seems harder, it would require to have a lock on the file to be sure that no one modify the file, same for a webpage. > Dear all, > > At the moment, a discussion on haskell-cafe is going on > about how to neatly program the fact that an entire program > depends on a number of parameters that are read in once at > the beginning of a program. > > The suggestion that many people came up with was using > unsafePerformIO in the beginning to read the file. Here is > my version of that: > > | data Configuration = ... -- config data > | > | getConfig :: Configuration > | getConfig = unsafePerformIO $ > | do ...read configuration from file... > | return configuration > | > | main = > | do doStuff > > It is quite disturbing that there is no other easy way to do > this than using unsafePerformIO (except for using implicit > parameters perhaps, but there are other reasons for not > using those). > > I have been thinking a little bit more about this and here > is what I found. > > Remember the Gofer days, when Gofer had a "function": > > openFile :: FilePath -> String > > This was of course a cheap and dirty way of implementing > things like the getConfig above, but it is impure. However, > one could imagine a functional version of this function: > > readFileOnce :: FilePath -> Maybe String > > This function will read the contents of the file (and return > Nothing if something went wrong), but it is memoized, so > that the second time you use this function you get the same > result. > > So, it is a pure function. (Admittedly, it is somewhat > unpredictable, but you will always get the same result for > the same arguments.) It is no more strange than GHC's pure > version of the getArgs function (I forgot what it was/is > called). > > How about space behavior, you say? Reading a file, and > memoizing the result means storing the whole contents of the > file in memory! > > The point is that the use of this function will typically > happen at the beginning of a program, when reading the > configuration file(s). When all this has happened, the > function readFileOnce, and its memo table, will be garabage > collected. (Of course there is no guarantee that all calls > to readFileOnce will be evaluated at the beginning of a > program, and it is not required, but when you do, there are > no space problems.) > > There could of course be pure "-Once" versions of other IO > operations. Here is a list of possibilities: > > - reading a file > - getting arguments > - getting environment variables > - downloading a webpage > - ... > > What do you think? > > Regards, > /Koen. > > -- > Koen Claessen > http://www.cs.chalmers.se/~koen > Chalmers University, Gothenburg, Sweden. > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- Yoann Padioleau, INSA de Rennes, France, Opinions expressed here are only mine. Je n'�cris qu'� titre personnel. **____ Get Free. Be Smart. Simply use Linux and Free Software. ____** From nick.name@inwind.it Thu Sep 26 14:36:35 2002 From: nick.name@inwind.it (Nick Name) Date: Thu, 26 Sep 2002 15:36:35 +0200 Subject: Dealing with configuration data In-Reply-To: References: <20020926013314.5da489b7.nick.name@inwind.it> Message-ID: <20020926153635.1bd6ab30.nick.name@inwind.it> I just wrote a long and clear answer, but my e-mail client has crashed. I am going to change it (or to rewrite one in Haskell, grrr) but the answer will be shorter, I apologize. On Wed, 25 Sep 2002 16:34:02 -0700 (PDT) Hal Daume III wrote: > I don't mean to troll, but this isn't what I meant. You aren't. I misunderstood you, of course. > now, we have doStuff :: IO a. doStuff is allowed (even in its pure > methods) to use getConfig. I claim that this is safe. I could be > wrong; this is only a hand-waiving argument. Why? > > The first reference in the program to globalConfig is through a > writeIORef. This means that at this point globalConfig gets evaluated > and thus a ref is created. Immediately we put a value in it. > > Now, when doStuff runs, since it is an action run *after* the call to > writeIORef, provided that it doesn't also write to 'globalConfig' > (which I mentioned in my original message), any call to getConfig is > deterministic. Even this appears correct, and I feel that it's a technique widely used in the haskell community, nothing prevents a global optimizer to evaluate all pure functions wich do not depend on a value obtained by IO *before the "main" function*. This is also stated in the GHC documentation, about "unsafePerformIO": "If the I/O computation wrapped in unsafePerformIO performs side effects, then the relative order in which those side effects take place (relative to the main I/O trunk, or other calls to unsafePerformIO) is indeterminate." If getConfig is evaluated before the main function (nothing prevents it) and if all equal pure expressions are evaluated only once, readConfig will always lead to "undefined" (yes, it will always be evaluated after "globalConfig"). The first idea from Koen Claessen (getConfig operates directly on the file with unsafePerformIO) appears to work, but this time we are *relying* on the fact that the function will be evaluated once, since the file could change and multiple evaluations of readConfig wouldn't lead to the same result. This is not good anyway. Vincenzo From d95lars@dtek.chalmers.se Thu Sep 26 14:39:04 2002 From: d95lars@dtek.chalmers.se (Lars Lundgren) Date: Thu, 26 Sep 2002 15:39:04 +0200 (MEST) Subject: Pure File Reading (was: Dealing with configuration data) In-Reply-To: Message-ID: On 26 Sep 2002, Yoann Padioleau wrote: > Koen Claessen writes: > > i find your idea very good. > indeed for the library GetOpt, the argument of a program never change so it > make sense to make this library without using IO monad, same for argv and for the enviroment. > for openFile it seems harder, it would require to have a lock on the file > to be sure that no one modify the file, same for a webpage. > No, not at all. All that is required is to make sure all calls to openFile f returns the same string, i.e the contents of the file when it was read the first time. /Lars L From Yoann.Padioleau@irisa.fr Thu Sep 26 14:52:47 2002 From: Yoann.Padioleau@irisa.fr (Yoann Padioleau) Date: 26 Sep 2002 15:52:47 +0200 Subject: Pure File Reading (was: Dealing with configuration data) In-Reply-To: Lars Lundgren's message of "Thu, 26 Sep 2002 15:39:04 +0200 (MEST)" References: Message-ID: Lars Lundgren writes: > On 26 Sep 2002, Yoann Padioleau wrote: > > > Koen Claessen writes: > > > > i find your idea very good. > > indeed for the library GetOpt, the argument of a program never change so it > > make sense to make this library without using IO monad, same for argv and for the enviroment. > > > for openFile it seems harder, it would require to have a lock on the file > > to be sure that no one modify the file, same for a webpage. > > > > No, not at all. All that is required is to make sure all calls to openFile > f returns the same string, i.e the contents of the file when it was read > the first time. yes you are right. but it requires to change the name of the function to have Once appended to it. so in the Prelude, we should have 2 version of the same kind of fonction, one pure such as readFileOnce with a cool type, and one such as readFile with an Io type. Sounds good idea to me, cos many programs require just to read a file one time. i dont know if practically it is useful. after all we can do all the IO stuff in the main, and then continue in a pure world. dont know if it is useful to read a file in the middle of a pure function. > > /Lars L > > > -- Yoann Padioleau, INSA de Rennes, France, Opinions expressed here are only mine. Je n'�cris qu'� titre personnel. **____ Get Free. Be Smart. Simply use Linux and Free Software. ____** From koen@cs.chalmers.se Thu Sep 26 15:02:01 2002 From: koen@cs.chalmers.se (Koen Claessen) Date: Thu, 26 Sep 2002 16:02:01 +0200 (MET DST) Subject: Dealing with configuration data In-Reply-To: <20020926153635.1bd6ab30.nick.name@inwind.it> Message-ID: Nick Name wrote: | The first idea from Koen Claessen (getConfig operates | directly on the file with unsafePerformIO) appears to | work, but this time we are *relying* on the fact that | the function will be evaluated once, since the file | could change and multiple evaluations of readConfig | wouldn't lead to the same result. This is not good | anyway. But Hal Daume III's suggestion has that same problem: | data Configuration = ... -- config data | | globalConfig :: IORef Configuration | globalConfig = unsafePerformIO (newIORef undefined) : | getConfig :: Configuration | getConfig = unsafePerformIO $ readIORef globalConfig : | main = do | ...read configuration from file...no calls to getConfig... | writeIORef globalConfig configuration | doStuff | return () Imagine "globalConfig" being evaluated twice! This means there will be *two* IORefs in your program; one might be initialized, and not the other. This is even more disastrous. (To see what could happen: just inline the definition of globalConfig into the two places where it is used.) This is why one has to be EXTREMELY careful when using these kinds of constructs. Really, only use unsafePerformIO when you know what you are doing, and otherwise, leave it to someone else who can wrap it up into a nice, pure library. In general, when using unsafePerformIO in this way, one wants to tell the compiler that it is not allowed to inline the expression. This can be done in most compilers by giving compiler pragma's. /Koen. -- Koen Claessen http://www.cs.chalmers.se/~koen Chalmers University, Gothenburg, Sweden. From nick.name@inwind.it Thu Sep 26 15:40:32 2002 From: nick.name@inwind.it (Nick Name) Date: Thu, 26 Sep 2002 16:40:32 +0200 Subject: Dealing with configuration data In-Reply-To: References: <20020926153635.1bd6ab30.nick.name@inwind.it> Message-ID: <20020926164032.1863e2da.nick.name@inwind.it> On Thu, 26 Sep 2002 16:02:01 +0200 (MET DST) Koen Claessen wrote: > In general, when using unsafePerformIO in this way, one > wants to tell the compiler that it is not allowed to inline > the expression. This can be done in most compilers by giving > compiler pragma's. In the need of a mutable configuration, I prefer to use the IO monad anyway, because one of the reasons I am studying haskell is to stop having to bother with "inline" and/or order of evaluation. Vincenzo -- Fedeli alla linea, anche quando non c'� Quando l'imperatore � malato, quando muore,o � dubbioso, o � perplesso. Fedeli alla linea la linea non c'�. [CCCP] From hdaume@ISI.EDU Thu Sep 26 15:46:51 2002 From: hdaume@ISI.EDU (Hal Daume III) Date: Thu, 26 Sep 2002 07:46:51 -0700 (PDT) Subject: Dealing with configuration data In-Reply-To: Message-ID: Koen, > getConfig :: Configuration > getConfig = unsafePerformIO $ > do ...read configuration from file... > return configuration > > (*) Actually, a Haskell compiler is free to inline these > kind of expressions, so really one has to give a > NOINLINE pragma to the compiler as well. I'd always avoided this type of thing precisely because of the inline issue, which I don't think my version is in danger of. That's just me, though :). From rjmh@cs.chalmers.se Thu Sep 26 19:26:17 2002 From: rjmh@cs.chalmers.se (John Hughes) Date: Thu, 26 Sep 2002 20:26:17 +0200 (MET DST) Subject: Dealing with configuration data In-Reply-To: Message-ID: On Thu, 26 Sep 2002, Simon Peyton-Jones wrote: > | Sorry, I should also mention implicit parameters, if you're willing to > use > | that extension. I don't like them, though, and my impression from SPJ > is > | that it's very unclear whether they will get into Haskell 2 or not... > I wrote a short paper on this very topic, comparing alternative solutions. I ended up favouring implicit parameters. If you want to read it, it's at http://www.cs.chalmers.se/~rjmh/Globals.ps John From oleg@pobox.com Fri Sep 27 00:28:03 2002 From: oleg@pobox.com (oleg@pobox.com) Date: Thu, 26 Sep 2002 16:28:03 -0700 (PDT) Subject: Pure File Reading (was: Dealing with configuration data) References: Message-ID: <200209262328.QAA11313@adric.fnmoc.navy.mil> There is another solution to the problem of configurational parameters. The main part of the solution is portable, does not depend on any pragmas, does not use unsafe operations, does not use implicit parameters, and does not require any modifications to the user code. I must warn that it is also potentially vomit-inducing. It seems that the problem at hand naturally splits into two phases: building the configuration environment, and executing some code in that environment. The phases are executed sequentially. The facts suggest the use of a SupedMonad. SuperMonad is very well known and often used, even by people who never heard of simpler monads. The following code is an illustration. Suppose file '/tmp/a.hs' contains the following user code, which is to run within the configuration environment provided by the module Config. For simplicity, our configuration is made of one Int datum, config_item: >>> File "/tmp/a.hs" > import Config (config_item) > > foo = "foo shows: " ++ (show config_item) > > bar = "bar shows: " ++ (show config_item) > > main = do > print foo > print bar > print foo We specifically illustrate the reading of the config item several times. The following code runs the first phase: reads the configuration, build the SuperMonad and runs the SuperMonad. > import System (system, ExitCode(ExitSuccess)) > > myconfig_file = "/tmp/config" > > phaseII_var = "/tmp/Config.hs" > phaseII_const = "/tmp/a.hs" > > nl = "\n" > > writeConfig :: Int -> IO () > writeConfig num = > do > writeFile phaseII_var $ > concat > ["module Config (config_item) where", nl, > "config_item =", show num, nl] > > > runSuperIO () = system ("echo main | hugs " ++ phaseII_const) > >>= \ExitSuccess -> print "Phase II done" > > main = readFile myconfig_file >>= writeConfig . read >>= runSuperIO I did warn you, didn't I? I have a hunch this solution will work with GHC even better than it works with Hugs. Perhaps we can even play with some dynamic linking tricks (like shared object initializers, etc). BTW, the solution above is similar in spirit to the following trick in C++: Config config; int main() { /* pure functional C++ code here -- yes, it exists*/} the constructor for 'config' is guaranteed to run before main(). Perhaps someone will implement Staged Haskell one day? From liyang@nerv.cx Fri Sep 27 04:16:20 2002 From: liyang@nerv.cx (Liyang Hu) Date: Fri, 27 Sep 2002 04:16:20 +0100 Subject: Dealing with configuration data In-Reply-To: References: <20020926013314.5da489b7.nick.name@inwind.it> Message-ID: <20020927031620.GA13747@sakura.local.nerv.cx> --oJ71EGRlYNjSvfq7 Content-Type: multipart/mixed; boundary="wq9mPyueHGvFACwf" Content-Disposition: inline --wq9mPyueHGvFACwf Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Evening all, Thanks for all the replies and suggestions! They've been extremely helpful. On Wed, Sep 25, 2002 at 04:34:02PM -0700, Hal Daume III wrote: > Okay, this is "bad" but I claim it's okay, iff it is used as in: In the end, I opted for the global IORef through unsafePerformIO scheme; implicit parameters seemed too `bleedin' edge' for me... (that and I had in mind to also retro-fit the idea on top of WASH-CGI[0]; I don't want to make more changes than I absolutely have to.) (I haven't yet read John Hughes' paper on the topic though; that should be quite fun.) One thing to watch out for though: hGetContents is *not* your friend. At least it isn't if you're going to let it defer its work until you're inside modifyIORef... see the attached prefs.hs, line 28 onwards. Just for reference, I'm using GHC 5.02.2. I must have went almost insane trying to figure out why I was still getting the default settings, when every single line of the code seemed to state the contrary; I had already written up prefs.hs to post to the list to ask for help, when I noticed that if I put in the line ``mapM_ putStrLn kvs'' before I update the IORef, I get my new settings. If I leave it out, I get the defaults. Then it hit me -- hGetContents was lazily deferring its reads. A quickie alternative hGetLines seems to have fixed the problem. But I'm still not sure *why* that was a problem in the first place... Can anyone explain? (Looking at the library source didn't help.) Surely modifyIORef would have reduced kvs to head normal form (correct termino- logy?) just like putStrLn did? *sigh* This can't be good for my mental health. Thanks everyone, /Liyang BTW: I'm on both the main and -cafe lists; you don't have to CC me. ^_- [0] http://www.informatik.uni-freiburg.de/~thiemann/WASH/ --=20 =2E--{ Liyang HU }--{ http://nerv.cx/ }--{ Caius@Cam }--{ ICQ: 39391385 }--. | ``Computer games don't affect kids, I mean if Pac Man affected us as | | kids, we'd all be running around in darkened rooms, munching pills and | | listening to repetitive music.'' | --wq9mPyueHGvFACwf Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename="prefs.hs" module Main where import Prelude import Char ( isSpace, toLower ) import IO import IOExts ( IORef, modifyIORef, newIORef, readIORef, unsafePerformIO ) -- Bung everything inside a record, to save us multiple IORefs data Config = Config { cfgSomeSetting :: String } configRef = unsafePerformIO $ newIORef $ Config { cfgSomeSetting = "this is the default setting" } config = unsafePerformIO $ readIORef configRef -- as a shortcut / compatibility with existing code someSetting = cfgSomeSetting config -- returns lines in reverse order, I know, but it's irrelevant hGetLines h = get [] where get ls = (hGetLine h >>= get . (: ls)) `catch` (const $ return ls) -- *should* be called first thing in main (if at all); -- otherwise madness ensues... loadConfig :: FilePath -> IO () loadConfig conf = bracket (openFile conf ReadMode) hClose $ \ h -> do kvs <- fmap (map keyVal . filter isNotComment . lines) (hGetContents h) --kvs <- fmap (map keyVal . filter isNotComment) (hGetLines h) --mapM_ putStrLn kvs modifyIORef configRef (\ c -> foldl cfgLine c kvs) where keyVal s = (map toLower key, dropWhile isSpace rest) where (key, rest) = break isSpace s isNotComment ('#':_) = False isNotComment [] = False isNotComment _ = True cfgLine c ("setting", v) = c { cfgSomeSetting = v } cfgLine c _ = c -- ignore everything else main = do loadConfig "prefs.conf" local <- readIORef configRef mapM_ putStrLn [ cfgSomeSetting local, cfgSomeSetting config, someSetting ] --wq9mPyueHGvFACwf Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename="prefs.conf" # ignored setting overridden --wq9mPyueHGvFACwf Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename=Makefile GHC=ghc -O2 PACKAGES=-package lang SRC=prefs.hs all: $(SRC:.hs=) %: %.hs @$(GHC) --make $(@) -o $@ $(PACKAGES) $< clean: rm -f *.hi *.o $(SRC:.hs=) .PHONY: clean ghci --wq9mPyueHGvFACwf-- --oJ71EGRlYNjSvfq7 Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.6 (GNU/Linux) Comment: moo! (ID: 7B632CB8) iEYEARECAAYFAj2TzYQACgkQ1QR4EHtjLLg3JgCgwhm+pMumR6XdWTxz66/F2rya NrcAoI75ViSlKhwng0DsJBOBqsdSiC7f =IGrg -----END PGP SIGNATURE----- --oJ71EGRlYNjSvfq7-- From heringto@cs.unc.edu Fri Sep 27 17:56:38 2002 From: heringto@cs.unc.edu (Dean Herington) Date: Fri, 27 Sep 2002 12:56:38 -0400 Subject: Dealing with configuration data References: <20020925230636.GA30622@sakura.local.nerv.cx> <20020926010918.GA16066@smtp.alicorna.com> Message-ID: <3D948DC6.D3222A1D@cs.unc.edu> Andrew J Bromage wrote: > There's also a much uglier solution which I occasionally use if I > need an "ad hoc" global variable. Rather than using IORefs, I use > Strings as keys. The code is here: > > http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/hfl/hfl/ioext/ I'm not sure why you consider the code you refer to above so ugly. In any case, I have a question and a comment on it. Question: Why do you use `seq` on `globalTableRef`? Comment: You use `addToFM` to replace entries in your table. Without additional logic to increase strictness, I think you unnecessarily risk stack overflow. Consider the case where `writeIOGlobal` is used many times on a global between uses of `readIOGlobal` on that global. The above issue raises a general question: How should strictness best be achieved with `addToFM`? -- Dean From ajb@spamcop.net Sun Sep 29 02:00:28 2002 From: ajb@spamcop.net (Andrew J Bromage) Date: Sun, 29 Sep 2002 11:00:28 +1000 Subject: Dealing with configuration data In-Reply-To: <3D948DC6.D3222A1D@cs.unc.edu> References: <20020925230636.GA30622@sakura.local.nerv.cx> <20020926010918.GA16066@smtp.alicorna.com> <3D948DC6.D3222A1D@cs.unc.edu> Message-ID: <20020929010028.GA13399@smtp.alicorna.com> G'day all. On Fri, Sep 27, 2002 at 12:56:38PM -0400, Dean Herington wrote: > I'm not sure why you consider the code you refer to above so ugly. Anything which relies on unsafePerformIO (or seq, for that matter) is ugly. Personal opinion, of course. :-) > Question: > Why do you use `seq` on `globalTableRef`? Good question. It's actually a form of documentation. I wasn't 100% sure how concurrency and CAFs interact at the time (and I'm still not), so I left that in as a sort of note to myself to check this out. Admittedly a comment would have been clearer. :-) > You use `addToFM` to replace entries in your table. Without additional > logic to increase strictness, I think you unnecessarily risk stack > overflow. That's true, although the case of many writes followed by a single read I would expect to be rare in practice. Besides, IOGlobal is not designed for performance. It's designed for quick hacks. Cheers, Andrew Bromage From cdreklam@daldal.com Mon Sep 30 17:52:58 2002 From: cdreklam@daldal.com (Hayri DALDAL) Date: Mon, 30 Sep 2002 19:52:58 +0300 Subject: E-MaiL Bankas� Message-ID: <20020930165556.1C7ED421F56@www.haskell.org> =3Chtml=3E =3Chead=3E =3Ctitle=3ET=FCrk E-Mail Bank=3C=2Ftitle=3E =3Cmeta http-equiv=3D=22Content-Type=22 content=3D=22text=2Fhtml=3B charset=3Diso-8859-9=22=3E =3Cmeta http-equiv=3D=22Content-Type=22 content=3D=22text=2Fhtml=3B charset=3Dwindows-1254=22=3E =3C=2Fhead=3E =3Cbody bgcolor=3D=22#FFFFFF=22 text=3D=22#000000=22 leftmargin=3D=220=22 topmargin=3D=220=22 marginwidth=3D=220=22 marginheight=3D=220=22=3E =3Ctable width=3D=22630=22 border=3D=220=22 cellspacing=3D=220=22 cellpadding=3D=220=22 align=3D=22center=22 background=3D=22http=3A=2F=2Fcdreklam=2Edaldal=2Ecom=2Fbackchip2=2Ejpg=22=3E =3Ctr=3E =3Ctd valign=3D=22middle=22=3E =3Cblockquote=3E =3Cdiv align=3D=22right=22=3E=3C=2Fdiv=3E =3Cp align=3D=22right=22=3E=3Cfont face=3D=22Verdana=22 size=3D=222=22=3E=3Cb=3E=3Cfont color=3D=22#000099=22=3ET=FCrk E-Mail Bank =AE patentli=2C =22E-Mail Adres Rehberleri=22miz g=FCncellenmi=FEtir=3C=2Ffont=3E=3Cfont color=3D=22#FFCC00=22=3E=2E=3C=2Ffont=3E=3C=2Fb=3E=3C=2Ffont=3E=3C=2Fp=3E =3Cp align=3D=22right=22=3E=3Cfont face=3D=22Verdana=22 size=3D=222=22=3E Sekt=F6rler=2C iller=2C kurum ve kurulu=FElar=2C e=F0ilim ve ilgiler baz=FDnda kategorize edilmi=FE E-Mail Adres Rehberleri'mizle 5 Milyon yerli Internet kullan=FDc=FDs=FDna "=3B=3Cstrong=3Ebir anda=3C=2Fstrong=3E"=3B ula=FEabilir=3B=3Cbr=3E reklam=2C tan=FDt=FDm=2C duyuru=2C ilan ve her t=FCrl=FC kampanyalar=FDn=FDz=FD g=F6nderebilirsiniz=2E=3Cbr=3E =3C=2Ffont=3E=3C=2Fp=3E =3Cp align=3D=22center=22=3E=3Cfont face=3D=22Times New Roman=22=3E=3Cb=3E=3Cfont size=3D=225=22=3E5=2E000=2E000 YERLi E-MAIL REHBERi=3Cbr=3E =3Cfont color=3D=22#000000=22 size=3D=227=22=3E150 $=3C=2Ffont=3E=3C=2Ffont=3E=3Cfont size=3D=224=22=3E=3Cbr=3E =3Cfont size=3D=222=22 color=3D=22#FF0000=22=3ESaatte 80=2E000 mail yollayabilen Group Mail program=FD hediyeli=3C=2Ffont=3E=3C=2Ffont=3E=3C=2Fb=3E=3C=2Ffont=3E=3C=2Fp=3E =3Cp align=3D=22center=22=3E=3Cfont color=3D=22#003366=22 size=3D=223=22 face=3D=22Arial=22=3E=3Cstrong=3EGazete=2C Radyo ve Tv'lerin Traj ve Reatingiyle=3Cbr=3E Reklam Fiyatlar=FDyla Kar=FE=FDla=FEt=FDr=FDn Hangisi Karl=FD !=3C=2Fstrong=3E=3C=2Ffont=3E=3C=2Fp=3E =3Cp align=3D=22center=22=3E=3Cfont face=3D=22Verdana=22 size=3D=222=22=3E=3Cstrong=3EWeb=3A =3Ca href=3D=22http=3A=2F=2Fcdreklam=2Edaldal=2Ecom=22 target=3D=22=5Fblank=22=3Ecdreklam=2Edaldal=2Ecom=3C=2Fa=3E=3C=2Fstrong=3E=3C=2Ffont=3E=3C=2Fp=3E =3Cp align=3D=22right=22=3E=3Cfont face=3D=22Verdana=22 size=3D=222=22=3E Daha farkl=FD soru=2C g=F6r=FC=FE=2C teklif ve sipari=FEleriniz i=E7in bize ula=FEabilirsiniz=2E=3C=2Ffont=3E=3C=2Fp=3E =3Cp align=3D=22right=22=3E=3Cfont face=3D=22Verdana=22 size=3D=222=22=3EWeb Tasar=FDm=FD=2C Domain tescili ve Hosting fiyatlar=FDm=FDz=FD mutlaka sorun=2E=3C=2Ffont=3E=3C=2Fp=3E =3Cp align=3D=22right=22=3E=3Cfont face=3D=22Verdana=22 size=3D=222=22=3E=3Cb=3E=3Cfont color=3D=22#0000FF=22=3E"=3BKaaN Ajans Organizasyon=AE"=3B=3Cbr=3E Hayri DALDAL =28Koordinator=29 =3B=3C=2Ffont=3E=3C=2Fb=3E=3C=2Ffont=3E=3C=2Fp=3E =3Cp align=3D=22right=22=3E=3Cfont face=3D=22Verdana=22 size=3D=222=22=3E=3Cb=3ETEL=3A 0312 440 78 65=28PBX=29=3C=2Fb=3E=3C=2Ffont=3E=3Cfont face=3D=22Verdana=22 size=3D=222=22=3E=3Cb=3E=3Cbr=3E E-MaiL=3A =3Ca href=3D=22mailto=3Ahayri=40daldal=2Ecom=22=3Ehayri=40daldal=2Ecom=3C=2Fa=3E=3C=2Fb=3E=3C=2Ffont=3E=3C=2Fp=3E =3Cp align=3D=22right=22=3E=3Cfont face=3D=22Verdana=22 size=3D=222=22=3EBu ileti 5 Milyon Turk Internet kullan=FDc=FDs=FDn=FDn e-mail adresine g=F6nderilmi=FEtir=2E=3Cbr=3E =3C=2Ffont=3E=3C=2Fp=3E =3C=2Fblockquote=3E =3C=2Ftd=3E =3C=2Ftr=3E =3C=2Ftable=3E =3C=2Fbody=3E =3C=2Fhtml=3E