From byorgey at seas.upenn.edu  Sun Dec  1 03:21:27 2013
From: byorgey at seas.upenn.edu (Brent Yorgey)
Date: Sat, 30 Nov 2013 22:21:27 -0500
Subject: [Haskell-beginners] Equality instance for lists
In-Reply-To: <7410f2a45dd5.529a697b@dit.ie>
References: <7410f2a45dd5.529a697b@dit.ie>
Message-ID: <20131201032127.GA6944@seas.upenn.edu>

On Sat, Nov 30, 2013 at 10:40:59PM +0000, Patrick Browne wrote:
>    Hi,
>    I am trying to write my own simplified class and instances for equality.
>    I have trouble with the equality equation for the empty list.
>    Even though I can use the [] == [] at the GHCi prompt I cannot use it in
>    my equality test.
>    How can I make my eq test handle empty lists while staying within the
>    context of my current code?.
>    Thanks,
>    Pat
> 
>    class Eq1 a where
>     eq :: a -> a -> Bool
>     
>    instance Eq1 Int where
>     eq a b =  a == b
> 
>    instance Eq1 a => Eq1 [a] where
>    -- This line compiles but gives an run time error.
>     eq [] [] =  True

This code does not give a run time error.  The error you are getting
is a type inference error, which has nothing to do with this code.

>     eq [] []

You simply need to give a type annotation on one of the empty lists.

  eq ([] :: [Int]) []

The standard Eq class has some built-in magic support by GHCI
(extended default rules) which means this does not apply in the case
of using == directly.

-Brent

From willieekaputra at gmail.com  Sun Dec  1 07:22:12 2013
From: willieekaputra at gmail.com (willie ekaputra)
Date: Sun, 1 Dec 2013 08:22:12 +0100
Subject: [Haskell-beginners] This code does not work : conversion error
Message-ID: <CAMCAAFcOAmtvBMcZwdXW98AawV=rcthJns-rA0jDb6-C_4aiMg@mail.gmail.com>

Hi everyone !
I am newbie and I made this code for counting k, so that 2^k divisor of
n.Somehow it doesn't work.
Anyone knows what is  wrong?

Regards and thanks.
Wili.

maxexp2:: Int -> Int
maxexp2 n
    |n== 0 || 2^k 'mod' n /=0 =0
    |otherwise = k
          Where
           k= e ' div' f
           e=round (fromIntegral (log n))
            f = round (fromIntegral (log 2))
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From toad3k at gmail.com  Sun Dec  1 08:12:08 2013
From: toad3k at gmail.com (David McBride)
Date: Sun, 1 Dec 2013 03:12:08 -0500
Subject: [Haskell-beginners] This code does not work : conversion error
In-Reply-To: <CAMCAAFcOAmtvBMcZwdXW98AawV=rcthJns-rA0jDb6-C_4aiMg@mail.gmail.com>
References: <CAMCAAFcOAmtvBMcZwdXW98AawV=rcthJns-rA0jDb6-C_4aiMg@mail.gmail.com>
Message-ID: <CAN+Tr40So-N8jH97tF7a9-uqBk_2WjczdBeta8xQBfhbWPZqpg@mail.gmail.com>

You just have a few problems.  Where should be lowercase.  The single
quotes should be backticks "`".  You may have some indentation issues.  And
lastly, you have some problems with e and f

   e = round (log $ fromIntegral n)
   f = round (log 2)

Otherwise it seems fine.


On Sun, Dec 1, 2013 at 2:22 AM, willie ekaputra <willieekaputra at gmail.com>wrote:

> Hi everyone !
> I am newbie and I made this code for counting k, so that 2^k divisor of
> n.Somehow it doesn't work.
> Anyone knows what is  wrong?
>
> Regards and thanks.
> Wili.
>
> maxexp2:: Int -> Int
> maxexp2 n
>     |n== 0 || 2^k 'mod' n /=0 =0
>     |otherwise = k
>           Where
>            k= e ' div' f
>            e=round (fromIntegral (log n))
>             f = round (fromIntegral (log 2))
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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From mukeshtiwari.iiitm at gmail.com  Sun Dec  1 08:17:03 2013
From: mukeshtiwari.iiitm at gmail.com (mukesh tiwari)
Date: Sun, 1 Dec 2013 13:47:03 +0530
Subject: [Haskell-beginners] This code does not work : conversion error
In-Reply-To: <CAMCAAFcOAmtvBMcZwdXW98AawV=rcthJns-rA0jDb6-C_4aiMg@mail.gmail.com>
References: <CAMCAAFcOAmtvBMcZwdXW98AawV=rcthJns-rA0jDb6-C_4aiMg@mail.gmail.com>
Message-ID: <CAFHZvE9YRH3MTe88bYnY4ac00RaHH=bVqr5Wc_LLjOBPnWmgqA@mail.gmail.com>

Hi Willie,
Here is the code  modified
maxexp2:: Int -> Int
maxexp2 n
    |n== 0 || 2^k `mod` n /=0 =0
    |otherwise = k
          where
            k = e `div` f
            e  = round  ( log ( fromIntegral n ) )
            f = round ( (log 2.0 ))

When you computing  k then use backticks (`) [1]  not the single quote ( ' )

[1] http://book.realworldhaskell.org/read/functional-programming.html( See
Infix function )


On Sun, Dec 1, 2013 at 12:52 PM, willie ekaputra
<willieekaputra at gmail.com>wrote:

> Hi everyone !
> I am newbie and I made this code for counting k, so that 2^k divisor of
> n.Somehow it doesn't work.
> Anyone knows what is  wrong?
>
> Regards and thanks.
> Wili.
>
> maxexp2:: Int -> Int
> maxexp2 n
>     |n== 0 || 2^k 'mod' n /=0 =0
>     |otherwise = k
>           Where
>            k= e ' div' f
>            e=round (fromIntegral (log n))
>             f = round (fromIntegral (log 2))
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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From patrick.browne at dit.ie  Sun Dec  1 12:52:42 2013
From: patrick.browne at dit.ie (Patrick Browne)
Date: Sun, 1 Dec 2013 12:52:42 +0000
Subject: [Haskell-beginners] Equality instance for lists
In-Reply-To: <20131201032127.GA6944@seas.upenn.edu>
References: <7410f2a45dd5.529a697b@dit.ie>
 <20131201032127.GA6944@seas.upenn.edu>
Message-ID: <7470afb66035.529b311a@dit.ie>

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From math.simplex at gmail.com  Sun Dec  1 14:16:58 2013
From: math.simplex at gmail.com (Graham Gill)
Date: Sun, 01 Dec 2013 09:16:58 -0500
Subject: [Haskell-beginners] This code does not work : conversion error
In-Reply-To: <CAFHZvE9YRH3MTe88bYnY4ac00RaHH=bVqr5Wc_LLjOBPnWmgqA@mail.gmail.com>
References: <CAMCAAFcOAmtvBMcZwdXW98AawV=rcthJns-rA0jDb6-C_4aiMg@mail.gmail.com>
 <CAFHZvE9YRH3MTe88bYnY4ac00RaHH=bVqr5Wc_LLjOBPnWmgqA@mail.gmail.com>
Message-ID: <529B44DA.3020902@gmail.com>

Once you've made those changes, you also need

n `mod` 2^k

instead of 2^k `mod` n.

Finally, using e `div` f, and round() in the definitions of e and f, to 
give you the largest power of 2 dividing n doesn't work correctly. For 
example:
maxexp2 4 = 1 (should be 2)
maxexp2 16 = 3 (should be 4)
maxexp2 18 = 0 (should be 1)
maxexp2 28 = 0 (should be 2)

But that's not a Haskell error, that's a problem with the algorithm.

(Sorry if I've misinterpreted what you're trying to do.)

Graham

On 01/12/2013 3:17 AM, mukesh tiwari wrote:
> Hi Willie,
> Here is the code  modified
> maxexp2:: Int -> Int
> maxexp2 n
>     |n== 0 || 2^k `mod` n /=0 =0
>     |otherwise = k
>           where
>             k = e `div` f
>             e  = round  ( log ( fromIntegral n ) )
>             f = round ( (log 2.0 ))
>
> When you computing  k then use backticks (`) [1]  not the single quote 
> ( ' )
>
> [1] http://book.realworldhaskell.org/read/functional-programming.html( 
> <http://book.realworldhaskell.org/read/functional-programming.html%28> 
> See Infix function )
>
>
> On Sun, Dec 1, 2013 at 12:52 PM, willie ekaputra 
> <willieekaputra at gmail.com <mailto:willieekaputra at gmail.com>> wrote:
>
>     Hi everyone !
>     I am newbie and I made this code for counting k, so that 2^k
>     divisor of n.Somehow it doesn't work.
>     Anyone knows what is  wrong?
>
>     Regards and thanks.
>     Wili.
>
>     maxexp2:: Int -> Int
>     maxexp2 n
>         |n== 0 || 2^k 'mod' n /=0 =0
>         |otherwise = k
>               Where
>                k= e ' div' f
>                e=round (fromIntegral (log n))
>                 f = round (fromIntegral (log 2))
>
>
>     _______________________________________________
>     Beginners mailing list
>     Beginners at haskell.org <mailto:Beginners at haskell.org>
>     http://www.haskell.org/mailman/listinfo/beginners
>
>
>
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners

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From plredmond at gmail.com  Sun Dec  1 22:30:50 2013
From: plredmond at gmail.com (Patrick Redmond)
Date: Mon, 2 Dec 2013 11:30:50 +1300
Subject: [Haskell-beginners] Overflow when reading C types
Message-ID: <CAHUea4F6VDqLEFRJZME+RVMLa5+7FZ+xbw4nN9VMJL67TPPpnw@mail.gmail.com>

Prelude> import Foreign.C.Types
Prelude Foreign.C.Types> read "-10" :: CUInt
4294967286
Prelude Foreign.C.Types> read "300" :: CChar
44

This seems like a bug. Shouldn't these result in some kind of read error?

The values expressed as strings are simply not part of the type they
are being parsed into. However, Haskell seems to parse them into an
arbitrarily wide numeric type, and then overflow them down to the
correct size.

What's the rationale here?

From ml at extensibl.com  Sun Dec  1 22:38:33 2013
From: ml at extensibl.com (ml at extensibl.com)
Date: Mon, 2 Dec 2013 11:38:33 +1300
Subject: [Haskell-beginners] Overflow when reading C types
In-Reply-To: <CAHUea4F6VDqLEFRJZME+RVMLa5+7FZ+xbw4nN9VMJL67TPPpnw@mail.gmail.com>
References: <CAHUea4F6VDqLEFRJZME+RVMLa5+7FZ+xbw4nN9VMJL67TPPpnw@mail.gmail.com>
Message-ID: <20131201223833.GA2954@li165-50.members.linode.com>

On Mon, Dec 02, 2013 at 11:30:50AM +1300, Patrick Redmond wrote:
> Prelude> import Foreign.C.Types
> Prelude Foreign.C.Types> read "-10" :: CUInt
> 4294967286
> Prelude Foreign.C.Types> read "300" :: CChar
> 44
> 

CUInt? I would try CInt instead.

A.

From ml at extensibl.com  Sun Dec  1 23:09:30 2013
From: ml at extensibl.com (ml at extensibl.com)
Date: Mon, 2 Dec 2013 12:09:30 +1300
Subject: [Haskell-beginners] Overflow when reading C types
In-Reply-To: <20131201223833.GA2954@li165-50.members.linode.com>
References: <CAHUea4F6VDqLEFRJZME+RVMLa5+7FZ+xbw4nN9VMJL67TPPpnw@mail.gmail.com>
 <20131201223833.GA2954@li165-50.members.linode.com>
Message-ID: <20131201230930.GB2954@li165-50.members.linode.com>

On Mon, Dec 02, 2013 at 11:38:33AM +1300, ml at extensibl.com wrote:
> On Mon, Dec 02, 2013 at 11:30:50AM +1300, Patrick Redmond wrote:
> > Prelude> import Foreign.C.Types
> > Prelude Foreign.C.Types> read "-10" :: CUInt
> > 4294967286
> > Prelude Foreign.C.Types> read "300" :: CChar
> > 44
> > 
> 
> CUInt? I would try CInt instead.
> 

Whoops, that is not related to the original question, sorry.


From patrick.browne at dit.ie  Mon Dec  2 00:08:42 2013
From: patrick.browne at dit.ie (Patrick Browne)
Date: Mon, 2 Dec 2013 00:08:42 +0000
Subject: [Haskell-beginners] Understanding inheritance
Message-ID: <7470d5ac4ff.529bcf8a@dit.ie>

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From zhiwudazhanjiangshi at gmail.com  Mon Dec  2 07:53:22 2013
From: zhiwudazhanjiangshi at gmail.com (yi lu)
Date: Mon, 2 Dec 2013 15:53:22 +0800
Subject: [Haskell-beginners] How to save a bracket in this case?
Message-ID: <CAKcmqqz2yfN-E5TmVYRh_2RrxwRrLicn3Y+APv012sFhr6aQfQ@mail.gmail.com>

Hi,

I want to calculate
*(81/10)^2*.

However, after I typed *81/10*, I remembered to add a bracket to surround
*81/10*. Is there one way to do some trick to save this bracket?

Actually I can *Ctrl+A* to move to the first character of this line. I want
the other solution.

Yi
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From vikraman.choudhury at gmail.com  Mon Dec  2 08:09:50 2013
From: vikraman.choudhury at gmail.com (Vikraman)
Date: Mon, 2 Dec 2013 13:39:50 +0530
Subject: [Haskell-beginners] How to save a bracket in this case?
In-Reply-To: <CAKcmqqz2yfN-E5TmVYRh_2RrxwRrLicn3Y+APv012sFhr6aQfQ@mail.gmail.com>
References: <CAKcmqqz2yfN-E5TmVYRh_2RrxwRrLicn3Y+APv012sFhr6aQfQ@mail.gmail.com>
Message-ID: <20131202080950.GA11470@felicia.iitk.ac.in>

On Mon, Dec 02, 2013 at 03:53:22PM +0800, yi lu wrote:
> Hi,
> 
> I want to calculate
> *(81/10)^2*.
> 
> However, after I typed *81/10*, I remembered to add a bracket to surround
> *81/10*. Is there one way to do some trick to save this bracket?
> 
> Actually I can *Ctrl+A* to move to the first character of this line. I want
> the other solution.
> 

(1) 81/10 * 81/10
(2) Enter 81/10
    The result gets saved in it
    Now, it^2

-- 
Vikraman

From orclev at gmail.com  Mon Dec  2 14:21:02 2013
From: orclev at gmail.com (Kyle Murphy)
Date: Mon, 2 Dec 2013 09:21:02 -0500
Subject: [Haskell-beginners] Understanding inheritance
In-Reply-To: <7470d5ac4ff.529bcf8a@dit.ie>
References: <7470d5ac4ff.529bcf8a@dit.ie>
Message-ID: <CA+y6JcwHh1kODy-5eti+4Ay+QTie2mi4eTug+hba8S5X=FYkCw@mail.gmail.com>

I think you're headed down a path that's only going to cause you confusion.
You shouldn't think in OO terms like sub and super classes. Each class is
its own thing, they aren't sub and super classes in the OO sense. A class
my have a constraint applied to it such that any type that is an instance
of that class, must also be an instance of one or more other classes. That
constraint is what allows you to use functions that belong to other classes
inside of default function definitions. Semantically this behaves much like
inheritance in an OO language, however functionally it's very different.
On Dec 1, 2013 7:08 PM, "Patrick Browne" <patrick.browne at dit.ie> wrote:

> Hi,
> In the example below does the concept of inheritance only apply to classes
> and not instances?
> By inheritance I mean that a method in a sub-class can use a method from
> the super-class but not vice versa.
> Would the inclusion of instance contexts such as 'instance (Eq a, Show b)
> => MyClass a b' apply such inheritance semantics between LHS => RHS of
> instances?
> My current misunderstandings are in the comments.
> Thanks,
> Pat
> -- Any instance of SUPER must define the super method. The super method
> definition may use any function in scope on the RHS of equations.
> -- If the default method is defined in the class it may use any method in
> scope except those from the sub-class
> class SUPER a where
>  super :: a -> a
> -- Any instance of SUB must define sub. The sub method definition may use
> super or any function in scope on the RHS of equations
> class SUPER a => SUB a where
>   sub :: a -> a
>
> -- This instance defines super and can use sub because sub it is defined
> and is in scope
> instance SUPER Int  where
>  super n  = 1 + (sub n)
>
> -- This instance defines sub
> instance SUB Int  where
>  sub n = 6 +  n
>
> -- The Char instances differs from the Int instances in that the SUB uses
> super.
> instance SUPER Char where
>  super n  = 's'
>
> -- The use of super here because it is defined and is in scope.
> instance SUB Char where
>  sub n = super n
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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From poczta at emanuelkoczwara.pl  Mon Dec  2 14:35:53 2013
From: poczta at emanuelkoczwara.pl (Emanuel Koczwara)
Date: Mon, 02 Dec 2013 15:35:53 +0100
Subject: [Haskell-beginners] Understanding inheritance
In-Reply-To: <CA+y6JcwHh1kODy-5eti+4Ay+QTie2mi4eTug+hba8S5X=FYkCw@mail.gmail.com>
References: <7470d5ac4ff.529bcf8a@dit.ie>
 <CA+y6JcwHh1kODy-5eti+4Ay+QTie2mi4eTug+hba8S5X=FYkCw@mail.gmail.com>
Message-ID: <1385994953.13699.7.camel@emanuel-laptop>

Hi,

  From perspective of a haskell beginner coming from OOP:

  Tt's like interfaces. If a class supports interface X, then it must
also supports interface Y. That's all. It's a simple thing, but can be
complicated if you will try to understand it in OOP terms.

Emanuel



From plredmond at gmail.com  Mon Dec  2 22:05:06 2013
From: plredmond at gmail.com (Patrick Redmond)
Date: Tue, 3 Dec 2013 11:05:06 +1300
Subject: [Haskell-beginners] Overflow when reading C types
In-Reply-To: <20131201230930.GB2954@li165-50.members.linode.com>
References: <CAHUea4F6VDqLEFRJZME+RVMLa5+7FZ+xbw4nN9VMJL67TPPpnw@mail.gmail.com>
 <20131201223833.GA2954@li165-50.members.linode.com>
 <20131201230930.GB2954@li165-50.members.linode.com>
Message-ID: <CAHUea4G86KXSGD-+Km_R+i2pdTkB0NFW=Mfy8_6KzDa8DWX8_g@mail.gmail.com>

Yeah, the unsigned is to demonstrate how "-10" is being interpreted as a
number before being cast to an unsigned.

My question is: Why isn't this just a read/parse error? "-10" isn't a valid
representation for any value of the CUInt type.

On Monday, December 2, 2013, wrote:

> On Mon, Dec 02, 2013 at 11:38:33AM +1300, ml at extensibl.com <javascript:;>wrote:
> > On Mon, Dec 02, 2013 at 11:30:50AM +1300, Patrick Redmond wrote:
> > > Prelude> import Foreign.C.Types
> > > Prelude Foreign.C.Types> read "-10" :: CUInt
> > > 4294967286
> > > Prelude Foreign.C.Types> read "300" :: CChar
> > > 44
> > >
> >
> > CUInt? I would try CInt instead.
> >
>
> Whoops, that is not related to the original question, sorry.
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org <javascript:;>
> http://www.haskell.org/mailman/listinfo/beginners
>
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From michael at orlitzky.com  Mon Dec  2 22:09:22 2013
From: michael at orlitzky.com (Michael Orlitzky)
Date: Mon, 02 Dec 2013 17:09:22 -0500
Subject: [Haskell-beginners] Overflow when reading C types
In-Reply-To: <CAHUea4G86KXSGD-+Km_R+i2pdTkB0NFW=Mfy8_6KzDa8DWX8_g@mail.gmail.com>
References: <CAHUea4F6VDqLEFRJZME+RVMLa5+7FZ+xbw4nN9VMJL67TPPpnw@mail.gmail.com>
 <20131201223833.GA2954@li165-50.members.linode.com>
 <20131201230930.GB2954@li165-50.members.linode.com>
 <CAHUea4G86KXSGD-+Km_R+i2pdTkB0NFW=Mfy8_6KzDa8DWX8_g@mail.gmail.com>
Message-ID: <529D0512.7060206@orlitzky.com>

On 12/02/2013 05:05 PM, Patrick Redmond wrote:
> Yeah, the unsigned is to demonstrate how "-10" is being interpreted as a
> number before being cast to an unsigned.
> 
> My question is: Why isn't this just a read/parse error? "-10" isn't a
> valid representation for any value of the CUInt type.
> 

Sure it is,

  unsigned int x = -10;

If you don't want a CUInt, don't use a CUInt =)



From ml at isaac.cedarswampstudios.org  Mon Dec  2 23:14:20 2013
From: ml at isaac.cedarswampstudios.org (Isaac Dupree)
Date: Mon, 02 Dec 2013 18:14:20 -0500
Subject: [Haskell-beginners] Overflow when reading C types
In-Reply-To: <529D0512.7060206@orlitzky.com>
References: <CAHUea4F6VDqLEFRJZME+RVMLa5+7FZ+xbw4nN9VMJL67TPPpnw@mail.gmail.com>
 <20131201223833.GA2954@li165-50.members.linode.com>
 <20131201230930.GB2954@li165-50.members.linode.com>
 <CAHUea4G86KXSGD-+Km_R+i2pdTkB0NFW=Mfy8_6KzDa8DWX8_g@mail.gmail.com>
 <529D0512.7060206@orlitzky.com>
Message-ID: <529D144C.5070401@isaac.cedarswampstudios.org>

On 12/02/2013 05:09 PM, Michael Orlitzky wrote:
> On 12/02/2013 05:05 PM, Patrick Redmond wrote:
>> Yeah, the unsigned is to demonstrate how "-10" is being interpreted as a
>> number before being cast to an unsigned.
>>
>> My question is: Why isn't this just a read/parse error? "-10" isn't a
>> valid representation for any value of the CUInt type.
>>
>
> Sure it is,
>
>    unsigned int x = -10;
>
> If you don't want a CUInt, don't use a CUInt =)

That is a C integral->integral conversion.  A better comparison for 
Haskell "read", if you think C gets to define the Haskell conversion 
from Haskell string to C integral type, would be strtol()/strtoul(), 
which are standard C functions that convert from C string to C integral 
type.

strtol() saturates at LONG_MIN and LONG_MAX.
strtoul() saturates at ULONG_MAX and is modulo at 0 (the first time; if 
the number is too negative then it saturates to ULONG_MAX).
Both set errno to ERANGE when they saturate.

C conversions from floating-point to signed or unsigned integral also 
saturate.

Unsigned types being Z/nZ is mathematically sound, but C is not very 
dedicated to this interpretation.  Furthermore, C signed arithmetic is 
undefined behavior if you overflow.  Haskell is much more dedicated to 
thinking both signed and unsigned C types are modulo than C is.

I too am curious whether it would make more sense for Haskell 
read/readsPrec to fail to read out-of-range integers.

-Isaac


From daniel.is.fischer at googlemail.com  Tue Dec  3 00:14:09 2013
From: daniel.is.fischer at googlemail.com (Daniel Fischer)
Date: Tue, 03 Dec 2013 01:14:09 +0100
Subject: [Haskell-beginners] Overflow when reading C types
In-Reply-To: <529D144C.5070401@isaac.cedarswampstudios.org>
References: <CAHUea4F6VDqLEFRJZME+RVMLa5+7FZ+xbw4nN9VMJL67TPPpnw@mail.gmail.com>
 <529D0512.7060206@orlitzky.com>
 <529D144C.5070401@isaac.cedarswampstudios.org>
Message-ID: <1653050.Djmnj83oKT@linux-hpeb.site>

On Monday 02 December 2013, 18:14:20, Isaac Dupree wrote:
> C conversions from floating-point to signed or unsigned integral also 
> saturate.

Not really. Clause 6.3.1.4 is quite explicit:

"When a finite value of real floating type is converted to an integer type 
other than _Bool, the fractional part is discarded (i.e., the value is 
truncated toward zero). If the value of the integral part cannot be 
represented by the integer type, the behavior is undefined."

and adds a footnote to make it unmistakeably clear that the remaindering 
operation need not be carried out when the target type is unsigned.

> 
> Unsigned types being Z/nZ is mathematically sound, but C is not very 
> dedicated to this interpretation.

It's mandated in 6.2.5 (9),

"A computation involving unsigned operands can never overflow, because a 
result that cannot be represented by the resulting unsigned integer type is
reduced modulo the number that is one greater than the largest value that can 
be represented by the resulting type."

> Furthermore, C signed arithmetic is undefined behavior if you overflow.

That cannot be stressed too much.

From ml at isaac.cedarswampstudios.org  Tue Dec  3 02:40:01 2013
From: ml at isaac.cedarswampstudios.org (Isaac Dupree)
Date: Mon, 02 Dec 2013 21:40:01 -0500
Subject: [Haskell-beginners] Overflow when reading C types
In-Reply-To: <1653050.Djmnj83oKT@linux-hpeb.site>
References: <CAHUea4F6VDqLEFRJZME+RVMLa5+7FZ+xbw4nN9VMJL67TPPpnw@mail.gmail.com>
 <529D0512.7060206@orlitzky.com>
 <529D144C.5070401@isaac.cedarswampstudios.org>
 <1653050.Djmnj83oKT@linux-hpeb.site>
Message-ID: <529D4481.1040508@isaac.cedarswampstudios.org>

On 12/02/2013 07:14 PM, Daniel Fischer wrote:
> On Monday 02 December 2013, 18:14:20, Isaac Dupree wrote:
>> C conversions from floating-point to signed or unsigned integral also
>> saturate.
>
> Not really. Clause 6.3.1.4 is quite explicit:
>
> "When a finite value of real floating type is converted to an integer type
> other than _Bool, the fractional part is discarded (i.e., the value is
> truncated toward zero). If the value of the integral part cannot be
> represented by the integer type, the behavior is undefined."
>
> and adds a footnote to make it unmistakeably clear that the remaindering
> operation need not be carried out when the target type is unsigned.

Whoops! Thank you for correcting me.

>> Unsigned types being Z/nZ is mathematically sound, but C is not very
>> dedicated to this interpretation.
>
> It's mandated in 6.2.5 (9),
>
> "A computation involving unsigned operands can never overflow, because a
> result that cannot be represented by the resulting unsigned integer type is
> reduced modulo the number that is one greater than the largest value that can
> be represented by the resulting type."

Yes, indeed, C unsigned arithmetic *is* Z/nZ and that is lovely (when 
you want it, at least).

My point there was that some functions/operations specified by the C 
standard that are related to unsigned types, like conversion from 
strings (strtoul()) and floats (casting), aren't modulo 2^n.  I see 
that's a weak point since each of those only differ from modulo in error 
conditions (errno set, or undefined behaviour).  If C was as good as(?) 
Haskell it might use modulo for those conversions too.

-Isaac


From shaegis at gmail.com  Sun Dec  8 00:21:32 2013
From: shaegis at gmail.com (S. H. Aegis)
Date: Sun, 8 Dec 2013 09:21:32 +0900
Subject: [Haskell-beginners] How can I read package document?
Message-ID: <CAJp-Nqy2k=ibJRO54LNGrUUA-yVCg4vEH4cdEhhJAYgroiAGJw@mail.gmail.com>

Hi. I'm new to Haskell.
I installed Palindromes package through cabal.
But I don't know the usage of command.
(Not enough information on Home Page.)
How can I read document?
Thank you. =)
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From fuuzetsu at fuuzetsu.co.uk  Sun Dec  8 00:51:56 2013
From: fuuzetsu at fuuzetsu.co.uk (Mateusz Kowalczyk)
Date: Sun, 08 Dec 2013 00:51:56 +0000
Subject: [Haskell-beginners] How can I read package document?
In-Reply-To: <CAJp-Nqy2k=ibJRO54LNGrUUA-yVCg4vEH4cdEhhJAYgroiAGJw@mail.gmail.com>
References: <CAJp-Nqy2k=ibJRO54LNGrUUA-yVCg4vEH4cdEhhJAYgroiAGJw@mail.gmail.com>
Message-ID: <52A3C2AC.2080409@fuuzetsu.co.uk>

On 08/12/13 00:21, S. H. Aegis wrote:
> Hi. I'm new to Haskell.
> I installed Palindromes package through cabal.
> But I don't know the usage of command.
> (Not enough information on Home Page.)
> How can I read document?
> Thank you. =)
> 
> 
> 
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
> 
Usually you'd check the documentation on Hackage[1] and if that's not
enough, you'd seek help in the source itself[2]. In this case, there are
some comments in the source that might interest you.

[1]: http://hackage.haskell.org/package/palindromes
[2]:
http://hackage.haskell.org/package/palindromes-0.4/docs/src/Data-Algorithms-Palindromes-Palindromes.html

-- 
Mateusz K.

From shaegis at gmail.com  Sun Dec  8 05:23:58 2013
From: shaegis at gmail.com (S. H. Aegis)
Date: Sun, 8 Dec 2013 14:23:58 +0900
Subject: [Haskell-beginners] How can I read package document?
In-Reply-To: <52A3C2AC.2080409@fuuzetsu.co.uk>
References: <CAJp-Nqy2k=ibJRO54LNGrUUA-yVCg4vEH4cdEhhJAYgroiAGJw@mail.gmail.com>
 <52A3C2AC.2080409@fuuzetsu.co.uk>
Message-ID: <-2703127754525991104@unknownmsgid>

Thank you so much !
I wish have a nice day .

Sok H. Chang

2013. 12. 8. ?? 9:52 Mateusz Kowalczyk <fuuzetsu at fuuzetsu.co.uk> ??:

>> On 08/12/13 00:21, S. H. Aegis wrote:
>> Hi. I'm new to Haskell.
>> I installed Palindromes package through cabal.
>> But I don't know the usage of command.
>> (Not enough information on Home Page.)
>> How can I read document?
>> Thank you. =)
>>
>>
>>
>> _______________________________________________
>> Beginners mailing list
>> Beginners at haskell.org
>> http://www.haskell.org/mailman/listinfo/beginners
> Usually you'd check the documentation on Hackage[1] and if that's not
> enough, you'd seek help in the source itself[2]. In this case, there are
> some comments in the source that might interest you.
>
> [1]: http://hackage.haskell.org/package/palindromes
> [2]:
> http://hackage.haskell.org/package/palindromes-0.4/docs/src/Data-Algorithms-Palindromes-Palindromes.html
>
> --
> Mateusz K.
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners

From sammuel.coles at gmail.com  Sun Dec  8 08:13:32 2013
From: sammuel.coles at gmail.com (Sam Coles)
Date: Sun, 8 Dec 2013 02:13:32 -0600
Subject: [Haskell-beginners] How can I read package document?
In-Reply-To: <-2703127754525991104@unknownmsgid>
References: <CAJp-Nqy2k=ibJRO54LNGrUUA-yVCg4vEH4cdEhhJAYgroiAGJw@mail.gmail.com>
 <52A3C2AC.2080409@fuuzetsu.co.uk>
 <-2703127754525991104@unknownmsgid>
Message-ID: <CANoDC_Rh1bXHZJh9b58T1Dfz+8h1fJ+amUNGS5069oNiCYUStw@mail.gmail.com>

You can also run the commands below to generate the documentation. This is
very useful because some of the documentation on the new hackage is
broken/incomplete.

    cd ~/src
    cabal unpack palindromes #untars the package into a dir in the current
dir
    cd palindromes-0.4
    cabal configure
    cabal haddock #generates documentation
    cd dist/doc/html/palindromes/ #index.html is in this directory


On Sat, Dec 7, 2013 at 11:23 PM, S. H. Aegis <shaegis at gmail.com> wrote:

> Thank you so much !
> I wish have a nice day .
>
> Sok H. Chang
>
> 2013. 12. 8. ?? 9:52 Mateusz Kowalczyk <fuuzetsu at fuuzetsu.co.uk> ??:
>
> >> On 08/12/13 00:21, S. H. Aegis wrote:
> >> Hi. I'm new to Haskell.
> >> I installed Palindromes package through cabal.
> >> But I don't know the usage of command.
> >> (Not enough information on Home Page.)
> >> How can I read document?
> >> Thank you. =)
> >>
> >>
> >>
> >> _______________________________________________
> >> Beginners mailing list
> >> Beginners at haskell.org
> >> http://www.haskell.org/mailman/listinfo/beginners
> > Usually you'd check the documentation on Hackage[1] and if that's not
> > enough, you'd seek help in the source itself[2]. In this case, there are
> > some comments in the source that might interest you.
> >
> > [1]: http://hackage.haskell.org/package/palindromes
> > [2]:
> >
> http://hackage.haskell.org/package/palindromes-0.4/docs/src/Data-Algorithms-Palindromes-Palindromes.html
> >
> > --
> > Mateusz K.
> > _______________________________________________
> > Beginners mailing list
> > Beginners at haskell.org
> > http://www.haskell.org/mailman/listinfo/beginners
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
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From shaegis at gmail.com  Sun Dec  8 08:57:07 2013
From: shaegis at gmail.com (S. H. Aegis)
Date: Sun, 8 Dec 2013 17:57:07 +0900
Subject: [Haskell-beginners] How can I read package document?
In-Reply-To: <CANoDC_Rh1bXHZJh9b58T1Dfz+8h1fJ+amUNGS5069oNiCYUStw@mail.gmail.com>
References: <CAJp-Nqy2k=ibJRO54LNGrUUA-yVCg4vEH4cdEhhJAYgroiAGJw@mail.gmail.com>
 <52A3C2AC.2080409@fuuzetsu.co.uk> <-2703127754525991104@unknownmsgid>
 <CANoDC_Rh1bXHZJh9b58T1Dfz+8h1fJ+amUNGS5069oNiCYUStw@mail.gmail.com>
Message-ID: <-1553686211342827818@unknownmsgid>

Thank you so much.
This is what I want. =)
Have a nice day.

Sok H. Chang

2013. 12. 8. ?? 5:13 Sam Coles <sammuel.coles at gmail.com> ??:

You can also run the commands below to generate the documentation. This is
very useful because some of the documentation on the new hackage is
broken/incomplete.

    cd ~/src
    cabal unpack palindromes #untars the package into a dir in the current
dir
    cd palindromes-0.4
    cabal configure
    cabal haddock #generates documentation
    cd dist/doc/html/palindromes/ #index.html is in this directory


On Sat, Dec 7, 2013 at 11:23 PM, S. H. Aegis <shaegis at gmail.com> wrote:

> Thank you so much !
> I wish have a nice day .
>
> Sok H. Chang
>
> 2013. 12. 8. ?? 9:52 Mateusz Kowalczyk <fuuzetsu at fuuzetsu.co.uk> ??:
>
> >> On 08/12/13 00:21, S. H. Aegis wrote:
> >> Hi. I'm new to Haskell.
> >> I installed Palindromes package through cabal.
> >> But I don't know the usage of command.
> >> (Not enough information on Home Page.)
> >> How can I read document?
> >> Thank you. =)
> >>
> >>
> >>
> >> _______________________________________________
> >> Beginners mailing list
> >> Beginners at haskell.org
> >> http://www.haskell.org/mailman/listinfo/beginners
> > Usually you'd check the documentation on Hackage[1] and if that's not
> > enough, you'd seek help in the source itself[2]. In this case, there are
> > some comments in the source that might interest you.
> >
> > [1]: http://hackage.haskell.org/package/palindromes
> > [2]:
> >
> http://hackage.haskell.org/package/palindromes-0.4/docs/src/Data-Algorithms-Palindromes-Palindromes.html
> >
> > --
> > Mateusz K.
> > _______________________________________________
> > Beginners mailing list
> > Beginners at haskell.org
> > http://www.haskell.org/mailman/listinfo/beginners
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>

_______________________________________________
Beginners mailing list
Beginners at haskell.org
http://www.haskell.org/mailman/listinfo/beginners
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From michaeltbaker at gmail.com  Mon Dec  9 21:11:36 2013
From: michaeltbaker at gmail.com (Michael Baker)
Date: Mon, 9 Dec 2013 15:11:36 -0600
Subject: [Haskell-beginners] Cabal build dependency using a git repo
Message-ID: <CACwW0Ub8PADFGbqAzi4EF_8S=YBFO94ec8uo9n4iuWJVa+AHVw@mail.gmail.com>

I have a library which isn't on Hackage that I would like to use as a build
dependency in another project. In Rubygems you can provide a git repository
in the absence of an actual Rubygems repository.

Does Cabal support something like that? I would like to specify that a
particular build depend can be fetched from a given git repository rather
than from Hackage and have Cabal fetch it when installing the build
dependencies.

I'm guessing that it's not possible because I don't see a mention of this
feature anywhere. If it's not possible, how do people typically handle this
problem? Git submodules?
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From mlists at pmade.com  Mon Dec  9 21:45:07 2013
From: mlists at pmade.com (Peter Jones)
Date: Mon, 09 Dec 2013 14:45:07 -0700
Subject: [Haskell-beginners] Cabal build dependency using a git repo
References: <CACwW0Ub8PADFGbqAzi4EF_8S=YBFO94ec8uo9n4iuWJVa+AHVw@mail.gmail.com>
Message-ID: <87a9g9lmvw.fsf@pmade.com>

Michael Baker <michaeltbaker at gmail.com> writes:
> I have a library which isn't on Hackage that I would like to use as a build
> dependency in another project. In Rubygems you can provide a git repository
> in the absence of an actual Rubygems repository.

Use a git submodule (or place the source code to the package anywhere on
your file system) then use `cabal sandbox add-source <path>`.  Provided
of course that you're using cabal sandboxes.

-- 
Peter Jones, Founder, Devalot.com
Defending the honor of good code


From michaeltbaker at gmail.com  Mon Dec  9 23:02:56 2013
From: michaeltbaker at gmail.com (Michael Baker)
Date: Mon, 9 Dec 2013 17:02:56 -0600
Subject: [Haskell-beginners] Cabal build dependency using a git repo
In-Reply-To: <87a9g9lmvw.fsf@pmade.com>
References: <CACwW0Ub8PADFGbqAzi4EF_8S=YBFO94ec8uo9n4iuWJVa+AHVw@mail.gmail.com>
 <87a9g9lmvw.fsf@pmade.com>
Message-ID: <CACwW0UYN5A-xh9Xxxa0mkSGmm3Ov73Sc_gKXpffKwBQ1EK7MjA@mail.gmail.com>

On Mon, Dec 9, 2013 at 3:45 PM, Peter Jones <mlists at pmade.com> wrote:
>
> Michael Baker <michaeltbaker at gmail.com> writes:
> > I have a library which isn't on Hackage that I would like to use as a
build
> > dependency in another project. In Rubygems you can provide a git
repository
> > in the absence of an actual Rubygems repository.
>
> Use a git submodule (or place the source code to the package anywhere on
> your file system) then use `cabal sandbox add-source <path>`.  Provided
> of course that you're using cabal sandboxes.

What is commonly done if you aren't using sandboxes? I would rather not use
them in an effort to make installing this project easier on my users,
because the current Haskell Platform doesn't have sandboxes yet.
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From fuuzetsu at fuuzetsu.co.uk  Tue Dec 10 01:23:50 2013
From: fuuzetsu at fuuzetsu.co.uk (Mateusz Kowalczyk)
Date: Tue, 10 Dec 2013 01:23:50 +0000
Subject: [Haskell-beginners] Cabal build dependency using a git repo
In-Reply-To: <CACwW0UYN5A-xh9Xxxa0mkSGmm3Ov73Sc_gKXpffKwBQ1EK7MjA@mail.gmail.com>
References: <CACwW0Ub8PADFGbqAzi4EF_8S=YBFO94ec8uo9n4iuWJVa+AHVw@mail.gmail.com>
 <87a9g9lmvw.fsf@pmade.com>
 <CACwW0UYN5A-xh9Xxxa0mkSGmm3Ov73Sc_gKXpffKwBQ1EK7MjA@mail.gmail.com>
Message-ID: <52A66D26.6010200@fuuzetsu.co.uk>

On 09/12/13 23:02, Michael Baker wrote:
> On Mon, Dec 9, 2013 at 3:45 PM, Peter Jones <mlists at pmade.com> wrote:
>>
>> Michael Baker <michaeltbaker at gmail.com> writes:
>>> I have a library which isn't on Hackage that I would like to use as a
> build
>>> dependency in another project. In Rubygems you can provide a git
> repository
>>> in the absence of an actual Rubygems repository.
>>
>> Use a git submodule (or place the source code to the package anywhere on
>> your file system) then use `cabal sandbox add-source <path>`.  Provided
>> of course that you're using cabal sandboxes.
> 
> What is commonly done if you aren't using sandboxes? I would rather not use
> them in an effort to make installing this project easier on my users,
> because the current Haskell Platform doesn't have sandboxes yet.
> 
> 
> 
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
> 
Sandboxes are for development. If you really want to make it easy for
your users, publish your other package to Hackage. If that's not an
option, perhaps require them to install the other package manually
first? Maybe provide a script which fetches sources and cabal installs.

-- 
Mateusz K.

From miroslav.karpis at gmail.com  Tue Dec 10 05:13:36 2013
From: miroslav.karpis at gmail.com (Miro Karpis)
Date: Tue, 10 Dec 2013 06:13:36 +0100
Subject: [Haskell-beginners] setting up haskell-mode in gnu-emacs (OSX)
Message-ID: <CAJnnbxHertwK-hPcpMfnmU0otUUB1m7AdtjoOZBG_cZBcuZ9hA@mail.gmail.com>

Hi,
I'm having troubles to set-up haskell-mode in gnu-emacs. I'm new to
emacs,...

Instructions says: via package manager add: M-x package-install <RET>
haskell-mode <RET>

I can open package manager, but where should I paste the command?

Thanks,
m.
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From allbery.b at gmail.com  Tue Dec 10 05:27:37 2013
From: allbery.b at gmail.com (Brandon Allbery)
Date: Tue, 10 Dec 2013 00:27:37 -0500
Subject: [Haskell-beginners] setting up haskell-mode in gnu-emacs (OSX)
In-Reply-To: <CAJnnbxHertwK-hPcpMfnmU0otUUB1m7AdtjoOZBG_cZBcuZ9hA@mail.gmail.com>
References: <CAJnnbxHertwK-hPcpMfnmU0otUUB1m7AdtjoOZBG_cZBcuZ9hA@mail.gmail.com>
Message-ID: <CAKFCL4W9E+X_CMtXQvzbS34itbiJ=e_yBkksL3KT3fdd9=pJ_w@mail.gmail.com>

On Tue, Dec 10, 2013 at 12:13 AM, Miro Karpis <miroslav.karpis at gmail.com>wrote:

> I'm having troubles to set-up haskell-mode in gnu-emacs. I'm new to
> emacs,...
> Instructions says: via package manager add: M-x package-install <RET>
> haskell-mode <RET>
> I can open package manager, but where should I paste the command?
>

That's not really pasteable as such.

M-x refers to pressing Meta-x (for a terminal this may not be available
without special configuration) or Esc followed by x. <RET> is the Return
key.

So:  press Esc, x (minibuffer shows "M-x "), type "package-install", press
Return, type "haskell-mode", press Return. (If you have configured Terminal
to use Option for Meta --- this is not default as it disables
internationalization --- then you can press Option-x instead of Esc
followed by x.)

-- 
brandon s allbery kf8nh                               sine nomine associates
allbery.b at gmail.com                                  ballbery at sinenomine.net
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net
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From miroslav.karpis at gmail.com  Tue Dec 10 06:19:15 2013
From: miroslav.karpis at gmail.com (Miro Karpis)
Date: Tue, 10 Dec 2013 07:19:15 +0100
Subject: [Haskell-beginners] setting up haskell-mode in gnu-emacs (OSX)
In-Reply-To: <CAKFCL4W9E+X_CMtXQvzbS34itbiJ=e_yBkksL3KT3fdd9=pJ_w@mail.gmail.com>
References: <CAJnnbxHertwK-hPcpMfnmU0otUUB1m7AdtjoOZBG_cZBcuZ9hA@mail.gmail.com>
 <CAKFCL4W9E+X_CMtXQvzbS34itbiJ=e_yBkksL3KT3fdd9=pJ_w@mail.gmail.com>
Message-ID: <CAJnnbxEWYK177Xq0cd1e-aM+9ABU+q5G+0LA_8gw9x7RVpaE7g@mail.gmail.com>

Thanks,

now I'm getting "Install package: haskell-mode[No match]". I'm doing this
via gnu-emacs in OSX

Do I need to download the package and place it somewhere?

Thanks,
m.


On Tue, Dec 10, 2013 at 6:27 AM, Brandon Allbery <allbery.b at gmail.com>wrote:

> On Tue, Dec 10, 2013 at 12:13 AM, Miro Karpis <miroslav.karpis at gmail.com>wrote:
>
>> I'm having troubles to set-up haskell-mode in gnu-emacs. I'm new to
>> emacs,...
>> Instructions says: via package manager add: M-x package-install <RET>
>> haskell-mode <RET>
>> I can open package manager, but where should I paste the command?
>>
>
> That's not really pasteable as such.
>
> M-x refers to pressing Meta-x (for a terminal this may not be available
> without special configuration) or Esc followed by x. <RET> is the Return
> key.
>
> So:  press Esc, x (minibuffer shows "M-x "), type "package-install", press
> Return, type "haskell-mode", press Return. (If you have configured Terminal
> to use Option for Meta --- this is not default as it disables
> internationalization --- then you can press Option-x instead of Esc
> followed by x.)
>
> --
> brandon s allbery kf8nh                               sine nomine
> associates
> allbery.b at gmail.com
> ballbery at sinenomine.net
> unix, openafs, kerberos, infrastructure, xmonad
> http://sinenomine.net
>
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From voldermort at hotmail.com  Tue Dec 10 09:28:06 2013
From: voldermort at hotmail.com (harry)
Date: Tue, 10 Dec 2013 09:28:06 +0000 (UTC)
Subject: [Haskell-beginners] download latest version of cabal-install from
	hackage
Message-ID: <loom.20131210T102648-551@post.gmane.org>

I'm trying to write a script that will download and install the latest
version of cabal-install. However, I can't find a URL to automatically fetch
the latest version. How can this be done?


From zhiwudazhanjiangshi at gmail.com  Tue Dec 10 09:43:07 2013
From: zhiwudazhanjiangshi at gmail.com (yi lu)
Date: Tue, 10 Dec 2013 17:43:07 +0800
Subject: [Haskell-beginners] download latest version of cabal-install
	from hackage
In-Reply-To: <loom.20131210T102648-551@post.gmane.org>
References: <loom.20131210T102648-551@post.gmane.org>
Message-ID: <CAKcmqqz8M+kNMBY5mh5jBiyg9t0d30gsGkyZWuw9eDDYOyRDCw@mail.gmail.com>

Click any package in hackage http://hackage.haskell.org/package/data-aviary

See what it will download.

Remember the package dependencies.

Yi


On Tue, Dec 10, 2013 at 5:28 PM, harry <voldermort at hotmail.com> wrote:

> I'm trying to write a script that will download and install the latest
> version of cabal-install. However, I can't find a URL to automatically
> fetch
> the latest version. How can this be done?
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
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From voldermort at hotmail.com  Tue Dec 10 10:16:57 2013
From: voldermort at hotmail.com (harry)
Date: Tue, 10 Dec 2013 10:16:57 +0000 (UTC)
Subject: [Haskell-beginners]
	=?utf-8?q?download_latest_version_of_cabal-in?=
	=?utf-8?q?stall=09from_hackage?=
References: <loom.20131210T102648-551@post.gmane.org>
 <CAKcmqqz8M+kNMBY5mh5jBiyg9t0d30gsGkyZWuw9eDDYOyRDCw@mail.gmail.com>
Message-ID: <loom.20131210T111408-310@post.gmane.org>

yi lu <zhiwudazhanjiangshi <at> gmail.com> writes:

> Click any package in hackage http://hackage.haskell.org/package/data-aviary
> See what it will download. 
> Remember the package dependencies.
> Yi
> 
> 
> On Tue, Dec 10, 2013 at 5:28 PM, harry <voldermort <at> hotmail.com>
wrote:I'm trying to write a script that will download and install the latest
> version of cabal-install. However, I can't find a URL to automatically fetch
> the latest version. How can this be done?

That's good for humans :)

I'm trying to download the latest version of the tar.gz from a script. I
guess I could scrape the URL from
http://hackage.haskell.org/package/cabal-install, but I'm looking for a
cleaner solution.


From zhiwudazhanjiangshi at gmail.com  Tue Dec 10 11:12:03 2013
From: zhiwudazhanjiangshi at gmail.com (yi lu)
Date: Tue, 10 Dec 2013 19:12:03 +0800
Subject: [Haskell-beginners] download latest version of cabal-install
	from hackage
In-Reply-To: <loom.20131210T111408-310@post.gmane.org>
References: <loom.20131210T102648-551@post.gmane.org>
 <CAKcmqqz8M+kNMBY5mh5jBiyg9t0d30gsGkyZWuw9eDDYOyRDCw@mail.gmail.com>
 <loom.20131210T111408-310@post.gmane.org>
Message-ID: <CAKcmqqx2vZo-TQ4c6H4G1vF-kC9G8-X4U3a7jXqZM+TLquhirw@mail.gmail.com>

In ~/.cabal/pachages/hackage.haskell.org/ folder, there is a list of files
in 00-index.tar.gz .

For example http://hackage.haskell.org/package/data-aviary , there is a
folder `data-aviary`. In it, there are folders `0.4.0`, `0.2.3` ...

In http://hackage.haskell.org/package/data-aviary , the download link is
http://hackage.haskell.org/package/data-aviary-0.4.0/data-aviary-0.4.0.tar.gz

So now, can you infer something from this?

Yi


On Tue, Dec 10, 2013 at 6:16 PM, harry <voldermort at hotmail.com> wrote:

> yi lu <zhiwudazhanjiangshi <at> gmail.com> writes:
>
> > Click any package in hackage
> http://hackage.haskell.org/package/data-aviary
> > See what it will download.
> > Remember the package dependencies.
> > Yi
> >
> >
> > On Tue, Dec 10, 2013 at 5:28 PM, harry <voldermort <at> hotmail.com>
> wrote:I'm trying to write a script that will download and install the
> latest
> > version of cabal-install. However, I can't find a URL to automatically
> fetch
> > the latest version. How can this be done?
>
> That's good for humans :)
>
> I'm trying to download the latest version of the tar.gz from a script. I
> guess I could scrape the URL from
> http://hackage.haskell.org/package/cabal-install, but I'm looking for a
> cleaner solution.
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
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From mlists at pmade.com  Tue Dec 10 15:44:19 2013
From: mlists at pmade.com (Peter Jones)
Date: Tue, 10 Dec 2013 08:44:19 -0700
Subject: [Haskell-beginners] Cabal build dependency using a git repo
References: <CACwW0Ub8PADFGbqAzi4EF_8S=YBFO94ec8uo9n4iuWJVa+AHVw@mail.gmail.com>
 <87a9g9lmvw.fsf@pmade.com>
 <CACwW0UYN5A-xh9Xxxa0mkSGmm3Ov73Sc_gKXpffKwBQ1EK7MjA@mail.gmail.com>
Message-ID: <87siu0k8x8.fsf@pmade.com>

Michael Baker <michaeltbaker at gmail.com> writes:
> On Mon, Dec 9, 2013 at 3:45 PM, Peter Jones <mlists at pmade.com> wrote:
>>
>> Michael Baker <michaeltbaker at gmail.com> writes:
>> > I have a library which isn't on Hackage that I would like to use as a
> build
>> > dependency in another project. In Rubygems you can provide a git
> repository
>> > in the absence of an actual Rubygems repository.
>>
>> Use a git submodule (or place the source code to the package anywhere on
>> your file system) then use `cabal sandbox add-source <path>`.  Provided
>> of course that you're using cabal sandboxes.
>
> What is commonly done if you aren't using sandboxes? I would rather
> not use them in an effort to make installing this project easier on my
> users, because the current Haskell Platform doesn't have sandboxes
> yet.

I believe it's possible to run your own installation of the Hackage
server or at least host packages on a web server under a specific
directory structure.  You can then configure cabal to fetch packages
from your private Hackage mirror.  Then you just host your private
packages and any necessary public packages.  More details:

  http://comonad.com/reader/2012/hackage-mirror/

-- 
Peter Jones, Founder, Devalot.com
Defending the honor of good code


From michaeltbaker at gmail.com  Tue Dec 10 15:55:35 2013
From: michaeltbaker at gmail.com (Michael Baker)
Date: Tue, 10 Dec 2013 09:55:35 -0600
Subject: [Haskell-beginners] Cabal build dependency using a git repo
In-Reply-To: <87siu0k8x8.fsf@pmade.com>
References: <CACwW0Ub8PADFGbqAzi4EF_8S=YBFO94ec8uo9n4iuWJVa+AHVw@mail.gmail.com>
 <87a9g9lmvw.fsf@pmade.com>
 <CACwW0UYN5A-xh9Xxxa0mkSGmm3Ov73Sc_gKXpffKwBQ1EK7MjA@mail.gmail.com>
 <87siu0k8x8.fsf@pmade.com>
Message-ID: <CACwW0UasboqCgoYh3JpM_-=Mq6+fyQCg0MK3YW0hoh9GNHzw4w@mail.gmail.com>

Ok, I'll try that. Thanks.


On Tue, Dec 10, 2013 at 9:44 AM, Peter Jones <mlists at pmade.com> wrote:

> Michael Baker <michaeltbaker at gmail.com> writes:
> > On Mon, Dec 9, 2013 at 3:45 PM, Peter Jones <mlists at pmade.com> wrote:
> >>
> >> Michael Baker <michaeltbaker at gmail.com> writes:
> >> > I have a library which isn't on Hackage that I would like to use as a
> > build
> >> > dependency in another project. In Rubygems you can provide a git
> > repository
> >> > in the absence of an actual Rubygems repository.
> >>
> >> Use a git submodule (or place the source code to the package anywhere on
> >> your file system) then use `cabal sandbox add-source <path>`.  Provided
> >> of course that you're using cabal sandboxes.
> >
> > What is commonly done if you aren't using sandboxes? I would rather
> > not use them in an effort to make installing this project easier on my
> > users, because the current Haskell Platform doesn't have sandboxes
> > yet.
>
> I believe it's possible to run your own installation of the Hackage
> server or at least host packages on a web server under a specific
> directory structure.  You can then configure cabal to fetch packages
> from your private Hackage mirror.  Then you just host your private
> packages and any necessary public packages.  More details:
>
>   http://comonad.com/reader/2012/hackage-mirror/
>
> --
> Peter Jones, Founder, Devalot.com
> Defending the honor of good code
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
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From miroslav.karpis at gmail.com  Wed Dec 11 08:40:41 2013
From: miroslav.karpis at gmail.com (Miro Karpis)
Date: Wed, 11 Dec 2013 09:40:41 +0100
Subject: [Haskell-beginners] aquamacs - history interpreter
Message-ID: <CAJnnbxF=K4J9A9toVfSC-H64-W-eF43o6aK=8-SXZGyPXzEyoA@mail.gmail.com>

Hi, please,..... I have started to use aquamacs and their haskell
interpreter. Only problem is that I don't know how to access interpreter
commands history. Usually it would be key UP/DOWN, but that will move the
cursor UP/DOWN. So,... please how can I access interpreter/console user
commands history in aquamacs?

Cheers,
Miro
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From fuuzetsu at fuuzetsu.co.uk  Wed Dec 11 08:46:01 2013
From: fuuzetsu at fuuzetsu.co.uk (Mateusz Kowalczyk)
Date: Wed, 11 Dec 2013 08:46:01 +0000
Subject: [Haskell-beginners] aquamacs - history interpreter
In-Reply-To: <CAJnnbxF=K4J9A9toVfSC-H64-W-eF43o6aK=8-SXZGyPXzEyoA@mail.gmail.com>
References: <CAJnnbxF=K4J9A9toVfSC-H64-W-eF43o6aK=8-SXZGyPXzEyoA@mail.gmail.com>
Message-ID: <52A82649.1050908@fuuzetsu.co.uk>

On 11/12/13 08:40, Miro Karpis wrote:
> Hi, please,..... I have started to use aquamacs and their haskell
> interpreter. Only problem is that I don't know how to access interpreter
> commands history. Usually it would be key UP/DOWN, but that will move the
> cursor UP/DOWN. So,... please how can I access interpreter/console user
> commands history in aquamacs?
> 
> Cheers,
> Miro
> 
> 
> 
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
> 
Try M-p. C-c C-l seems to bring up input history.

-- 
Mateusz K.

From miroslav.karpis at gmail.com  Wed Dec 11 09:00:11 2013
From: miroslav.karpis at gmail.com (Miro Karpis)
Date: Wed, 11 Dec 2013 10:00:11 +0100
Subject: [Haskell-beginners] aquamacs - history interpreter
In-Reply-To: <52A82649.1050908@fuuzetsu.co.uk>
References: <CAJnnbxF=K4J9A9toVfSC-H64-W-eF43o6aK=8-SXZGyPXzEyoA@mail.gmail.com>
 <52A82649.1050908@fuuzetsu.co.uk>
Message-ID: <CAJnnbxEWKDi5bfyXBQvNQVOsqHEA+rGL1zkV58OrR2-Rd8h69A@mail.gmail.com>

thanks but am new new emacs/aquamacs. What you mean by M-p C-c C-l.
Btw: am on OSX

Cheers,
Miro


On Wed, Dec 11, 2013 at 9:46 AM, Mateusz Kowalczyk
<fuuzetsu at fuuzetsu.co.uk>wrote:

> On 11/12/13 08:40, Miro Karpis wrote:
> > Hi, please,..... I have started to use aquamacs and their haskell
> > interpreter. Only problem is that I don't know how to access interpreter
> > commands history. Usually it would be key UP/DOWN, but that will move the
> > cursor UP/DOWN. So,... please how can I access interpreter/console user
> > commands history in aquamacs?
> >
> > Cheers,
> > Miro
> >
> >
> >
> > _______________________________________________
> > Beginners mailing list
> > Beginners at haskell.org
> > http://www.haskell.org/mailman/listinfo/beginners
> >
> Try M-p. C-c C-l seems to bring up input history.
>
> --
> Mateusz K.
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
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From mukeshtiwari.iiitm at gmail.com  Wed Dec 11 09:10:28 2013
From: mukeshtiwari.iiitm at gmail.com (mukesh tiwari)
Date: Wed, 11 Dec 2013 14:40:28 +0530
Subject: [Haskell-beginners] aquamacs - history interpreter
In-Reply-To: <CAJnnbxEWKDi5bfyXBQvNQVOsqHEA+rGL1zkV58OrR2-Rd8h69A@mail.gmail.com>
References: <CAJnnbxF=K4J9A9toVfSC-H64-W-eF43o6aK=8-SXZGyPXzEyoA@mail.gmail.com>
 <52A82649.1050908@fuuzetsu.co.uk>
 <CAJnnbxEWKDi5bfyXBQvNQVOsqHEA+rGL1zkV58OrR2-Rd8h69A@mail.gmail.com>
Message-ID: <CAFHZvE89LPiuTaCkOzMQ4Dyq2p-6vo_kzZf+=BWq66iic4t1zQ@mail.gmail.com>

On Wed, Dec 11, 2013 at 2:30 PM, Miro Karpis <miroslav.karpis at gmail.com>wrote:

> thanks but am new new emacs/aquamacs. What you mean by M-p C-c C-l.
> Btw: am on OSX
>

 I think M should be the Escape ( M-p is Escape followed by p ), C is
control ( C-c is controlled followed by c ).


> Cheers,
> Miro
>
>
> On Wed, Dec 11, 2013 at 9:46 AM, Mateusz Kowalczyk <
> fuuzetsu at fuuzetsu.co.uk> wrote:
>
>> On 11/12/13 08:40, Miro Karpis wrote:
>> > Hi, please,..... I have started to use aquamacs and their haskell
>> > interpreter. Only problem is that I don't know how to access interpreter
>> > commands history. Usually it would be key UP/DOWN, but that will move
>> the
>> > cursor UP/DOWN. So,... please how can I access interpreter/console user
>> > commands history in aquamacs?
>> >
>> > Cheers,
>> > Miro
>> >
>> >
>> >
>> > _______________________________________________
>> > Beginners mailing list
>> > Beginners at haskell.org
>> > http://www.haskell.org/mailman/listinfo/beginners
>> >
>> Try M-p. C-c C-l seems to bring up input history.
>>
>> --
>> Mateusz K.
>> _______________________________________________
>> Beginners mailing list
>> Beginners at haskell.org
>> http://www.haskell.org/mailman/listinfo/beginners
>>
>
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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From miroslav.karpis at gmail.com  Wed Dec 11 09:22:10 2013
From: miroslav.karpis at gmail.com (Miro Karpis)
Date: Wed, 11 Dec 2013 10:22:10 +0100
Subject: [Haskell-beginners] aquamacs - history interpreter
In-Reply-To: <CAFHZvE89LPiuTaCkOzMQ4Dyq2p-6vo_kzZf+=BWq66iic4t1zQ@mail.gmail.com>
References: <CAJnnbxF=K4J9A9toVfSC-H64-W-eF43o6aK=8-SXZGyPXzEyoA@mail.gmail.com>
 <52A82649.1050908@fuuzetsu.co.uk>
 <CAJnnbxEWKDi5bfyXBQvNQVOsqHEA+rGL1zkV58OrR2-Rd8h69A@mail.gmail.com>
 <CAFHZvE89LPiuTaCkOzMQ4Dyq2p-6vo_kzZf+=BWq66iic4t1zQ@mail.gmail.com>
Message-ID: <CAJnnbxH+Dooq97n2LgVzzaqTzDJfJJxtJW653MghdQk29zyMBA@mail.gmail.com>

many thanks: it actually is M-p (cursor up) and M-n (cursor down)

found it here:
http://www.stephenwalker.com/notes/aquamacsemacs-key-binding-list/

m.


On Wed, Dec 11, 2013 at 10:10 AM, mukesh tiwari <
mukeshtiwari.iiitm at gmail.com> wrote:

>
>
>
> On Wed, Dec 11, 2013 at 2:30 PM, Miro Karpis <miroslav.karpis at gmail.com>wrote:
>
>> thanks but am new new emacs/aquamacs. What you mean by M-p C-c C-l.
>> Btw: am on OSX
>>
>
>  I think M should be the Escape ( M-p is Escape followed by p ), C is
> control ( C-c is controlled followed by c ).
>
>
>> Cheers,
>> Miro
>>
>>
>> On Wed, Dec 11, 2013 at 9:46 AM, Mateusz Kowalczyk <
>> fuuzetsu at fuuzetsu.co.uk> wrote:
>>
>>> On 11/12/13 08:40, Miro Karpis wrote:
>>> > Hi, please,..... I have started to use aquamacs and their haskell
>>> > interpreter. Only problem is that I don't know how to access
>>> interpreter
>>> > commands history. Usually it would be key UP/DOWN, but that will move
>>> the
>>> > cursor UP/DOWN. So,... please how can I access interpreter/console user
>>> > commands history in aquamacs?
>>> >
>>> > Cheers,
>>> > Miro
>>> >
>>> >
>>> >
>>> > _______________________________________________
>>> > Beginners mailing list
>>> > Beginners at haskell.org
>>> > http://www.haskell.org/mailman/listinfo/beginners
>>> >
>>> Try M-p. C-c C-l seems to bring up input history.
>>>
>>> --
>>> Mateusz K.
>>> _______________________________________________
>>> Beginners mailing list
>>> Beginners at haskell.org
>>> http://www.haskell.org/mailman/listinfo/beginners
>>>
>>
>>
>> _______________________________________________
>> Beginners mailing list
>> Beginners at haskell.org
>> http://www.haskell.org/mailman/listinfo/beginners
>>
>>
>
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From miroslav.karpis at gmail.com  Wed Dec 11 14:06:22 2013
From: miroslav.karpis at gmail.com (Miro Karpis)
Date: Wed, 11 Dec 2013 15:06:22 +0100
Subject: [Haskell-beginners] autocomplete in haskell-aquamacs interpreter
Message-ID: <CAJnnbxH1-pk3gJJQGiMk=h1CfhvoiHd8SP7zGvVqCtrMDXBQhg@mail.gmail.com>

Please, is there a shortcut for autocomplete in aquamacs (for files and
haskell functions)?

Cheers,
m.
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From jhenahan at uvm.edu  Thu Dec 12 01:13:45 2013
From: jhenahan at uvm.edu (Jack Henahan)
Date: Wed, 11 Dec 2013 20:13:45 -0500
Subject: [Haskell-beginners] setting up haskell-mode in gnu-emacs (OSX)
In-Reply-To: <CAJnnbxEWYK177Xq0cd1e-aM+9ABU+q5G+0LA_8gw9x7RVpaE7g@mail.gmail.com>
References: <CAJnnbxHertwK-hPcpMfnmU0otUUB1m7AdtjoOZBG_cZBcuZ9hA@mail.gmail.com>
 <CAKFCL4W9E+X_CMtXQvzbS34itbiJ=e_yBkksL3KT3fdd9=pJ_w@mail.gmail.com>
 <CAJnnbxEWYK177Xq0cd1e-aM+9ABU+q5G+0LA_8gw9x7RVpaE7g@mail.gmail.com>
Message-ID: <8F46F32A-C5AF-426B-8696-E90102266878@uvm.edu>

You might not have the right package archive available. Try

    M-x package-list-packages

And then see if haskell-mode is listed. If not, you?ll need to add

    require 'package)
    (add-to-list 'package-archives 
        '("marmalade" .
          "http://marmalade-repo.org/packages/"
    ))
    (package-initialize)

to your .emacs (or the equivalent statement for MELPA).


On Dec 10, 2013, at 1:19 AM, Miro Karpis <miroslav.karpis at gmail.com> wrote:

> Thanks, 
> 
> now I'm getting "Install package: haskell-mode[No match]". I'm doing this via gnu-emacs in OSX
> 
> Do I need to download the package and place it somewhere?
> 
> Thanks,
> m.
> 
> 
> On Tue, Dec 10, 2013 at 6:27 AM, Brandon Allbery <allbery.b at gmail.com> wrote:
> On Tue, Dec 10, 2013 at 12:13 AM, Miro Karpis <miroslav.karpis at gmail.com> wrote:
> I'm having troubles to set-up haskell-mode in gnu-emacs. I'm new to emacs,...
> Instructions says: via package manager add: M-x package-install <RET> haskell-mode <RET>
> I can open package manager, but where should I paste the command?
> 
> That's not really pasteable as such.
> 
> M-x refers to pressing Meta-x (for a terminal this may not be available without special configuration) or Esc followed by x. <RET> is the Return key.
> 
> So:  press Esc, x (minibuffer shows "M-x "), type "package-install", press Return, type "haskell-mode", press Return. (If you have configured Terminal to use Option for Meta --- this is not default as it disables internationalization --- then you can press Option-x instead of Esc followed by x.)
> 
> -- 
> brandon s allbery kf8nh                               sine nomine associates
> allbery.b at gmail.com                                  ballbery at sinenomine.net
> unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net
> 
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners

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From jhenahan at uvm.edu  Thu Dec 12 01:19:01 2013
From: jhenahan at uvm.edu (Jack Henahan)
Date: Wed, 11 Dec 2013 20:19:01 -0500
Subject: [Haskell-beginners] Cabal build dependency using a git repo
In-Reply-To: <CACwW0UasboqCgoYh3JpM_-=Mq6+fyQCg0MK3YW0hoh9GNHzw4w@mail.gmail.com>
References: <CACwW0Ub8PADFGbqAzi4EF_8S=YBFO94ec8uo9n4iuWJVa+AHVw@mail.gmail.com>
 <87a9g9lmvw.fsf@pmade.com>
 <CACwW0UYN5A-xh9Xxxa0mkSGmm3Ov73Sc_gKXpffKwBQ1EK7MjA@mail.gmail.com>
 <87siu0k8x8.fsf@pmade.com>
 <CACwW0UasboqCgoYh3JpM_-=Mq6+fyQCg0MK3YW0hoh9GNHzw4w@mail.gmail.com>
Message-ID: <DE4D50ED-AA7D-4909-A586-82A66D0F94AA@uvm.edu>

I honestly recommend a sandbox. That is exactly the scenario they are used in, 
and there is no effect on your users since it?s just a local development concern.

On Dec 10, 2013, at 10:55 AM, Michael Baker <michaeltbaker at gmail.com> wrote:

> Ok, I'll try that. Thanks.
> 
> 
> On Tue, Dec 10, 2013 at 9:44 AM, Peter Jones <mlists at pmade.com> wrote:
> Michael Baker <michaeltbaker at gmail.com> writes:
> > On Mon, Dec 9, 2013 at 3:45 PM, Peter Jones <mlists at pmade.com> wrote:
> >>
> >> Michael Baker <michaeltbaker at gmail.com> writes:
> >> > I have a library which isn't on Hackage that I would like to use as a
> > build
> >> > dependency in another project. In Rubygems you can provide a git
> > repository
> >> > in the absence of an actual Rubygems repository.
> >>
> >> Use a git submodule (or place the source code to the package anywhere on
> >> your file system) then use `cabal sandbox add-source <path>`.  Provided
> >> of course that you're using cabal sandboxes.
> >
> > What is commonly done if you aren't using sandboxes? I would rather
> > not use them in an effort to make installing this project easier on my
> > users, because the current Haskell Platform doesn't have sandboxes
> > yet.
> 
> I believe it's possible to run your own installation of the Hackage
> server or at least host packages on a web server under a specific
> directory structure.  You can then configure cabal to fetch packages
> from your private Hackage mirror.  Then you just host your private
> packages and any necessary public packages.  More details:
> 
>   http://comonad.com/reader/2012/hackage-mirror/
> 
> --
> Peter Jones, Founder, Devalot.com
> Defending the honor of good code
> 
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
> 
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners

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From habari.zerglings at gmail.com  Fri Dec 13 15:25:03 2013
From: habari.zerglings at gmail.com (Matt R)
Date: Fri, 13 Dec 2013 15:25:03 +0000
Subject: [Haskell-beginners] Constrained polymorphic functions as
	natural transformations
In-Reply-To: <20131114135911.GA31874@seas.upenn.edu>
References: <CA+ixoL=c22yAzzzvx=-sXO4h2V=LmKegJN_4PJuqaSJ-cg-qSw@mail.gmail.com>
 <20131114135911.GA31874@seas.upenn.edu>
Message-ID: <CA+ixoL=VKs2yy2VrOUeWwWV7mFXY9ZOV5hoSdt3FHQOA18cx_A@mail.gmail.com>

Hi Brent,

Many thanks for taking the time to have a look! Hope you might be able to
cope with some more amateurish fumbling as I try and expand my
understanding...

On 14 November 2013 13:59, Brent Yorgey <byorgey at seas.upenn.edu> wrote:


> In general one must consider what are called
> *di*natural transformations.  (I ought to write a blog post about
> this.)...but I thought I would mention it in case you want to look it up
> later.


Thanks -- dinatural transformations are probably a bit beyond my comfort
zone right now, but I'll add it to my list of things to look at.

Interesting to discover that not all polymorphic functions are natural
transformations. "fix" seems rather exotic -- are there any less unusual
examples?

Note that you can't always characterize a type class by a single
> function like this.  For example, consider class Foo ... There is no way
> to pick functors f and g such that a Foo dictionary is
> equivalent to  f a -> g a.
>

I was wondering why the following wouldn't do the trick?

sig :: Foo a => Either Int a -> Either a Int
sig (Left n) = Left (bar n)
sig (Right a) = Right (baz a)


> This doesn't really make sense.  If a natural transformation
> consists of a family of arrows which all live in Hask_T,


In this case, I think the family of arrows lives in Hask -- we can
reinterpret our Hask endofunctors as instead being functors from Hask_T ->
Hask. Then there's no requirement on our constrained polymorphic functions
to commute with sig.

In your example function f, the two functors would be the identify functor
"Id" and a constant functor "K Foo", and naturality is just saying that,
for any function g: A -> B that satisfies show == show . f, then:

f = f . g

Which is clearly true for f.


Am I still barking up the wrong tree? Apologies if so, but it *feels* like
there should be something here, with the intuition that:

Functions that don't "inspect" their values ==> you can substitute values
without fundamentally affecting the action of the function ==> natural
transformations between Hask endofunctors.

Functions that don't inspect their values other than through a particular
interface T ==> you can substitute values without fundamentally affecting
the action of the function, providing your substitution is invisible
through the interface T ==> Natural transformations between functors Hask_T
-> Hask.

-- Matt
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From ky3 at atamo.com  Fri Dec 13 18:55:08 2013
From: ky3 at atamo.com (Kim-Ee Yeoh)
Date: Sat, 14 Dec 2013 01:55:08 +0700
Subject: [Haskell-beginners] Constrained polymorphic functions as
	natural transformations
In-Reply-To: <CA+ixoL=VKs2yy2VrOUeWwWV7mFXY9ZOV5hoSdt3FHQOA18cx_A@mail.gmail.com>
References: <CA+ixoL=c22yAzzzvx=-sXO4h2V=LmKegJN_4PJuqaSJ-cg-qSw@mail.gmail.com>
 <20131114135911.GA31874@seas.upenn.edu>
 <CA+ixoL=VKs2yy2VrOUeWwWV7mFXY9ZOV5hoSdt3FHQOA18cx_A@mail.gmail.com>
Message-ID: <CAPY+ZdQLCMuanaqPicS=_H1LwtycdEQS5C_8VrkaSyYBHai5Ow@mail.gmail.com>

On Fri, Dec 13, 2013 at 10:25 PM, Matt R <habari.zerglings at gmail.com> wrote:

> Interesting to discover that not all polymorphic functions are natural
> transformations. "fix" seems rather exotic -- are there any less unusual
> examples?


None of the church numerals of type (a -> a) -> (a -> a) are natural
transformations either:

zero _ = id
one f = f
two f = f . f
three f = f . f . f
etc.

-- Kim-Ee
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From andrew.fleckenstein at gmail.com  Fri Dec 13 21:03:23 2013
From: andrew.fleckenstein at gmail.com (Andrew Fleckenstein)
Date: Fri, 13 Dec 2013 16:03:23 -0500
Subject: [Haskell-beginners] Error with floats in implementation of Horner's
	method.
Message-ID: <CAAN9LwtawGc=dT5FDSjAokynvUnfm2R85QqYRHb0_7GyjWyWcw@mail.gmail.com>

Hi all,

I have implemented Horner's method for evaluating a polynomial as follows:

-- the nth horner element, given a list of coefficients and a value at
which it needs to be evaluated

horner_element l x n
    | n == (length l)-1 = last l
    | otherwise = (l !! n) + (horner_element l x (n+1))*x

-- compute a polynomial given as a list of coefficients at the value x
using horner's method.

horner l x = horner_element l x 0
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From andrew.fleckenstein at gmail.com  Fri Dec 13 21:07:42 2013
From: andrew.fleckenstein at gmail.com (Andrew Fleckenstein)
Date: Fri, 13 Dec 2013 16:07:42 -0500
Subject: [Haskell-beginners] Error with floats in implementation of
	Horner's method.
In-Reply-To: <CAAN9LwtawGc=dT5FDSjAokynvUnfm2R85QqYRHb0_7GyjWyWcw@mail.gmail.com>
References: <CAAN9LwtawGc=dT5FDSjAokynvUnfm2R85QqYRHb0_7GyjWyWcw@mail.gmail.com>
Message-ID: <CAAN9LwshL7sVkJBraaoy_cvGwBm5JNOx8oBC8nRHM+YGPni9Kg@mail.gmail.com>

And I have sent the email before it was finished, oops.

Evaluating at integer values works fine, but trying to do
*Main> let a = [-1,2,-6,2]
*Main> horner a 1.23

gives this error

<interactive>:4:10:
    No instance for (Fractional Integer)
      arising from the literal `1.23'
    Possible fix: add an instance declaration for (Fractional Integer)
    In the second argument of `horner', namely `1.23'
    In the expression: horner a 1.23
    In an equation for `it': it = horner a 1.23


I know it has something to do with types, but whenever I try to add a type
signature to the functions it just messes everything up even more. Any help
would be appreciated

Thanks,
Andrew



On Fri, Dec 13, 2013 at 4:03 PM, Andrew Fleckenstein <
andrew.fleckenstein at gmail.com> wrote:

> Hi all,
>
> I have implemented Horner's method for evaluating a polynomial as follows:
>
> -- the nth horner element, given a list of coefficients and a value at
> which it needs to be evaluated
>
> horner_element l x n
>     | n == (length l)-1 = last l
>     | otherwise = (l !! n) + (horner_element l x (n+1))*x
>
> -- compute a polynomial given as a list of coefficients at the value x
> using horner's method.
>
> horner l x = horner_element l x 0
>
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From ky3 at atamo.com  Fri Dec 13 21:20:52 2013
From: ky3 at atamo.com (Kim-Ee Yeoh)
Date: Sat, 14 Dec 2013 04:20:52 +0700
Subject: [Haskell-beginners] Error with floats in implementation of
 Horner's method.
In-Reply-To: <CAAN9LwshL7sVkJBraaoy_cvGwBm5JNOx8oBC8nRHM+YGPni9Kg@mail.gmail.com>
References: <CAAN9LwtawGc=dT5FDSjAokynvUnfm2R85QqYRHb0_7GyjWyWcw@mail.gmail.com>
 <CAAN9LwshL7sVkJBraaoy_cvGwBm5JNOx8oBC8nRHM+YGPni9Kg@mail.gmail.com>
Message-ID: <CAPY+ZdQzNzz4c=38+bQ7g0nOdzxZYEgC0Sqyh+9Otc35zA+zKw@mail.gmail.com>

On Sat, Dec 14, 2013 at 4:07 AM, Andrew Fleckenstein <
andrew.fleckenstein at gmail.com> wrote:

> I know it has something to do with types,


Right! :)


> but whenever I try to add a type signature to the functions it just messes
> everything up even more.


This works: let a :: [Double]; a = [-1,2,-6,2]

This works too: let a :: Num a => [a]; a = [-1,2,-6,2]

What do you think are the pros and cons of either?

-- Kim-Ee
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From andrew.fleckenstein at gmail.com  Fri Dec 13 21:51:25 2013
From: andrew.fleckenstein at gmail.com (Andrew Fleckenstein)
Date: Fri, 13 Dec 2013 16:51:25 -0500
Subject: [Haskell-beginners] Error with floats in implementation of
 Horner's method.
In-Reply-To: <CAPY+ZdQzNzz4c=38+bQ7g0nOdzxZYEgC0Sqyh+9Otc35zA+zKw@mail.gmail.com>
References: <CAAN9LwtawGc=dT5FDSjAokynvUnfm2R85QqYRHb0_7GyjWyWcw@mail.gmail.com>
 <CAAN9LwshL7sVkJBraaoy_cvGwBm5JNOx8oBC8nRHM+YGPni9Kg@mail.gmail.com>
 <CAPY+ZdQzNzz4c=38+bQ7g0nOdzxZYEgC0Sqyh+9Otc35zA+zKw@mail.gmail.com>
Message-ID: <CAAN9Lws7-bU+ajgAv1pMk5aTuSj5tV6gdSxvb_TjYVcKF7gQyg@mail.gmail.com>

I know Num is a class, and Double is an instance of the Num class. I guess
using Num would make it more generic, but I don't see why either one would
be better in this particular function.


On Fri, Dec 13, 2013 at 4:20 PM, Kim-Ee Yeoh <ky3 at atamo.com> wrote:

>
> On Sat, Dec 14, 2013 at 4:07 AM, Andrew Fleckenstein <
> andrew.fleckenstein at gmail.com> wrote:
>
>> I know it has something to do with types,
>
>
> Right! :)
>
>
>> but whenever I try to add a type signature to the functions it just
>> messes everything up even more.
>
>
> This works: let a :: [Double]; a = [-1,2,-6,2]
>
> This works too: let a :: Num a => [a]; a = [-1,2,-6,2]
>
> What do you think are the pros and cons of either?
>
> -- Kim-Ee
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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From byorgey at seas.upenn.edu  Sat Dec 14 02:21:32 2013
From: byorgey at seas.upenn.edu (Brent Yorgey)
Date: Fri, 13 Dec 2013 21:21:32 -0500
Subject: [Haskell-beginners] Error with floats in implementation of
 Horner's method.
In-Reply-To: <CAAN9Lws7-bU+ajgAv1pMk5aTuSj5tV6gdSxvb_TjYVcKF7gQyg@mail.gmail.com>
References: <CAAN9LwtawGc=dT5FDSjAokynvUnfm2R85QqYRHb0_7GyjWyWcw@mail.gmail.com>
 <CAAN9LwshL7sVkJBraaoy_cvGwBm5JNOx8oBC8nRHM+YGPni9Kg@mail.gmail.com>
 <CAPY+ZdQzNzz4c=38+bQ7g0nOdzxZYEgC0Sqyh+9Otc35zA+zKw@mail.gmail.com>
 <CAAN9Lws7-bU+ajgAv1pMk5aTuSj5tV6gdSxvb_TjYVcKF7gQyg@mail.gmail.com>
Message-ID: <20131214022132.GA17146@seas.upenn.edu>

Right.  The problem is that when you write

  let a = [1,2,3,4]

at the GHCi prompt, the Evil Monomorphism Restriction forces it to
have a monomorphic type, and GHCi picks [Integer].  I recommend that
you turn off the Monomorphism Restriction, which you can do in one of
the following ways:

  1) Type :set -XNoMonomorphismRestriction at the GHCi prompt
  2) Add :set -XNoMonomorphismRestriction to your ~/.ghci file.

If you do the latter then you only have to do it once, and from then
on the MR will always be turned off in GHCi.

With the MR turned off,

  let cs = [1,2,3,4]

will result in  cs :: Num a => [a]  which will work the way you expect.

-Brent


On Fri, Dec 13, 2013 at 04:51:25PM -0500, Andrew Fleckenstein wrote:
> I know Num is a class, and Double is an instance of the Num class. I guess
> using Num would make it more generic, but I don't see why either one would
> be better in this particular function.
> 
> 
> On Fri, Dec 13, 2013 at 4:20 PM, Kim-Ee Yeoh <ky3 at atamo.com> wrote:
> 
> >
> > On Sat, Dec 14, 2013 at 4:07 AM, Andrew Fleckenstein <
> > andrew.fleckenstein at gmail.com> wrote:
> >
> >> I know it has something to do with types,
> >
> >
> > Right! :)
> >
> >
> >> but whenever I try to add a type signature to the functions it just
> >> messes everything up even more.
> >
> >
> > This works: let a :: [Double]; a = [-1,2,-6,2]
> >
> > This works too: let a :: Num a => [a]; a = [-1,2,-6,2]
> >
> > What do you think are the pros and cons of either?
> >
> > -- Kim-Ee
> >
> > _______________________________________________
> > Beginners mailing list
> > Beginners at haskell.org
> > http://www.haskell.org/mailman/listinfo/beginners
> >
> >

> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners


From voldermort at hotmail.com  Mon Dec 16 20:19:39 2013
From: voldermort at hotmail.com (robert)
Date: Mon, 16 Dec 2013 20:19:39 +0000 (UTC)
Subject: [Haskell-beginners] strip --strip-unneeded on package libraries
Message-ID: <loom.20131216T211539-104@post.gmane.org>

I've noticed that installed packages all have a large .a archive which can
be shrunk by about 10% with strip --strip-unneeded. Is there any downside to
stripping, and if not, why isn't it done by GHC when the package is
installed? There's a (default) option for cabal-install to strip
executables, but it seems that package stripping has to be done manually,
each time.


From anguscomber at gmail.com  Fri Dec 20 18:00:08 2013
From: anguscomber at gmail.com (Angus Comber)
Date: Fri, 20 Dec 2013 18:00:08 +0000
Subject: [Haskell-beginners] Use of (n + 1) as parameter - is it more
	efficient?
Message-ID: <CAAtGUhX80Ro0Dvc8PrVWhLDcKjCWqyZPNAAW1vor6kf=y=jcpA@mail.gmail.com>

I created my own drop' function like this:

drop' :: Int -> [a] -> [a]
drop' 0 xs     = xs
drop' n []     = []
drop' n (x:xs) = drop' (n - 1) xs


But in the Haskell book I am reading it is written like this:

drop' :: Int -> [a] -> [a]
drop' 0 xs             = xs
drop' (n + 1) []       = []
drop' (n + 1) (x:xs) = drop' n xs

My version seems to work but I am concerned about my third line (drop' n []
    = []).  Is that a problem?

Why does this author use n + 1 as a parameter as opposed to n - 1 like I do
in body?

Or does it make no difference?
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From toad3k at gmail.com  Fri Dec 20 18:20:12 2013
From: toad3k at gmail.com (David McBride)
Date: Fri, 20 Dec 2013 13:20:12 -0500
Subject: [Haskell-beginners] Use of (n + 1) as parameter - is it more
	efficient?
In-Reply-To: <CAAtGUhX80Ro0Dvc8PrVWhLDcKjCWqyZPNAAW1vor6kf=y=jcpA@mail.gmail.com>
References: <CAAtGUhX80Ro0Dvc8PrVWhLDcKjCWqyZPNAAW1vor6kf=y=jcpA@mail.gmail.com>
Message-ID: <CAN+Tr43FrN8uybSs+sBZsaL-vn8OKx-DOO8zi1yGt59mFeoS0g@mail.gmail.com>

n+k patterns is a concept that used to be common in haskell but was later
determined to be a misfeature and now you have to explicitly enable it in
ghc.  It was kind of a fun thing that turned out not to be necessary.

The way that you do it is the way that it is recommended now and the code
generated should be identical.



On Fri, Dec 20, 2013 at 1:00 PM, Angus Comber <anguscomber at gmail.com> wrote:

> I created my own drop' function like this:
>
> drop' :: Int -> [a] -> [a]
> drop' 0 xs     = xs
> drop' n []     = []
> drop' n (x:xs) = drop' (n - 1) xs
>
>
> But in the Haskell book I am reading it is written like this:
>
> drop' :: Int -> [a] -> [a]
> drop' 0 xs             = xs
> drop' (n + 1) []       = []
> drop' (n + 1) (x:xs) = drop' n xs
>
> My version seems to work but I am concerned about my third line (drop' n
> []     = []).  Is that a problem?
>
> Why does this author use n + 1 as a parameter as opposed to n - 1 like I
> do in body?
>
> Or does it make no difference?
>
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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From vikraman.choudhury at gmail.com  Fri Dec 20 18:25:25 2013
From: vikraman.choudhury at gmail.com (Vikraman)
Date: Fri, 20 Dec 2013 23:55:25 +0530
Subject: [Haskell-beginners] Use of (n + 1) as parameter - is it more
 efficient?
In-Reply-To: <CAAtGUhX80Ro0Dvc8PrVWhLDcKjCWqyZPNAAW1vor6kf=y=jcpA@mail.gmail.com>
References: <CAAtGUhX80Ro0Dvc8PrVWhLDcKjCWqyZPNAAW1vor6kf=y=jcpA@mail.gmail.com>
Message-ID: <20131220182525.GA25506@felicia.cse.iitk.ac.in>

On Fri, Dec 20, 2013 at 06:00:08PM +0000, Angus Comber wrote:
> I created my own drop' function like this:
> 
> drop' :: Int -> [a] -> [a]
> drop' 0 xs     = xs
> drop' n []     = []
> drop' n (x:xs) = drop' (n - 1) xs
> 
> 
> But in the Haskell book I am reading it is written like this:
> 
> drop' :: Int -> [a] -> [a]
> drop' 0 xs             = xs
> drop' (n + 1) []       = []
> drop' (n + 1) (x:xs) = drop' n xs
> 
> My version seems to work but I am concerned about my third line (drop' n []
>     = []).  Is that a problem?
> 
> Why does this author use n + 1 as a parameter as opposed to n - 1 like I do
> in body?
> 
> Or does it make no difference?

Using (n + 1) in the pattern match will cause the match to fail for
negative numbers. But this would also need NPlusKPatterns.

Note that in your implementation, negative values will result in an
empty list, which is different from the GHC.List version.

drop n xs     | n <= 0 =  xs
drop _ []              =  []
drop n (_:xs)          =  drop (n-1) xs

You can easily find this out using quickcheck.

?> quickCheck $ \n xs -> drop' n xs == drop n xs

-- 
Vikraman
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From voldermort at hotmail.com  Sun Dec 22 14:38:53 2013
From: voldermort at hotmail.com (harry)
Date: Sun, 22 Dec 2013 14:38:53 +0000 (UTC)
Subject: [Haskell-beginners] retreive a list of installed packages
Message-ID: <loom.20131222T153649-617@post.gmane.org>

Is there any simple way for a program to retrieve a list of installed
packages (such as ghc-pkg list returns), or would it be easier to execute
phc-pkg as an external process and catch the output?


From kmandpjlynch at verizon.net  Sun Dec 22 17:23:42 2013
From: kmandpjlynch at verizon.net (Patrick Lynch)
Date: Sun, 22 Dec 2013 12:23:42 -0500
Subject: [Haskell-beginners] Is Cons in the Haskell Module Library
Message-ID: <869634CA9D1B4FF2A8ED6BB20D4A013E@UserPC>

Good morning,
I'm going through Graham Hutton's link on Category Theory [and yes I understand that you needn't study CT in order to use Haskell] and he uses Cons.
I realize that Cons may be a synonym for ':'.
But can someone tell me how to search the Haskell Library to find the module containing Cons?
Thank you and Merry Christmas
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From nadirsampaoli at gmail.com  Sun Dec 22 17:38:45 2013
From: nadirsampaoli at gmail.com (Nadir Sampaoli)
Date: Sun, 22 Dec 2013 18:38:45 +0100
Subject: [Haskell-beginners] Is Cons in the Haskell Module Library
In-Reply-To: <869634CA9D1B4FF2A8ED6BB20D4A013E@UserPC>
References: <869634CA9D1B4FF2A8ED6BB20D4A013E@UserPC>
Message-ID: <CAFYwTdQzsHmE9F1LPc_dAuhYzTnY37cyRo8bc6D761d401Ab=A@mail.gmail.com>

Hello Patrick,

> But can someone tell me how to search the Haskell Library to find the module
> containing Cons?

I (sadly) know nothing about Category Theory, so I probably am missing
something, but when I'm looking for the module where a function or
data type belongs to, I usually use Hoogle:
http://www.haskell.org/hoogle/ (there's a hoogle command-line tool
too).
Is it what you're after?

On a side note I tend to assimilate lisp's cons to Haskell's (:) too.
I wouldn't mind if someone corrects this view of mine in case it's not
correct :)


Regards,

Nadir

From vikraman.choudhury at gmail.com  Sun Dec 22 17:40:47 2013
From: vikraman.choudhury at gmail.com (Vikraman)
Date: Sun, 22 Dec 2013 23:10:47 +0530
Subject: [Haskell-beginners] Is Cons in the Haskell Module Library
In-Reply-To: <869634CA9D1B4FF2A8ED6BB20D4A013E@UserPC>
References: <869634CA9D1B4FF2A8ED6BB20D4A013E@UserPC>
Message-ID: <20131222174047.GA13334@felicia.cse.iitk.ac.in>

On Sun, Dec 22, 2013 at 12:23:42PM -0500, Patrick Lynch wrote:
> Good morning,
> I'm going through Graham Hutton's link on Category Theory [and yes I understand that you needn't study CT in order to use Haskell] and he uses Cons.
> I realize that Cons may be a synonym for ':'.
> But can someone tell me how to search the Haskell Library to find the module containing Cons?
> Thank you and Merry Christmas

Cons is (:) and is defined in GHC.Types.

?> :i (:)
data [] a = ... | a : [a]   -- Defined in `GHC.Types'
infixr 5 :

You could also try hoogle.

http://www.haskell.org/hoogle/?hoogle=cons

-- 
Vikraman
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From allbery.b at gmail.com  Sun Dec 22 17:51:13 2013
From: allbery.b at gmail.com (Brandon Allbery)
Date: Sun, 22 Dec 2013 12:51:13 -0500
Subject: [Haskell-beginners] Is Cons in the Haskell Module Library
In-Reply-To: <869634CA9D1B4FF2A8ED6BB20D4A013E@UserPC>
References: <869634CA9D1B4FF2A8ED6BB20D4A013E@UserPC>
Message-ID: <CAKFCL4XPk_-3_NFg0ykRmtLJfpzE_H6Dn-og5sm4PgJrFt8ndA@mail.gmail.com>

On Sun, Dec 22, 2013 at 12:23 PM, Patrick Lynch <kmandpjlynch at verizon.net>wrote:

>  Good morning,
> I'm going through Graham Hutton's link on Category Theory [and yes I
> understand that you needn't study CT in order to use Haskell] and he uses
> Cons.
> I realize that Cons may be a synonym for ':'.
> But can someone tell me how to search the Haskell Library to find the
> module containing Cons?
>

The usual point of Cons is that it's instructive to reconstruct the list
type from first principles. You would never do this in a real program,
since it's exactly the same as the built-in list type --- except that it
doesn't come with all the predefined list stuff, so it's easier for you to
build it yourself without interfering with (or being interfered with by!)
the standard library. It also doesn't come with the convenient syntactic
sugar. And even if for some reason you did need to restrict lists that way
in a real program, you would probably use a newtype instead so that you can
still use the standard list operations and syntax after unwrapping.

    data List a = Nil | Cons a (List a)
    data []   a = []  | (:)  a ([]   a) -- the builtin list type, for
comparison

-- 
brandon s allbery kf8nh                               sine nomine associates
allbery.b at gmail.com                                  ballbery at sinenomine.net
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net
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From byorgey at seas.upenn.edu  Sun Dec 22 20:26:50 2013
From: byorgey at seas.upenn.edu (Brent Yorgey)
Date: Sun, 22 Dec 2013 15:26:50 -0500
Subject: [Haskell-beginners] Constrained polymorphic functions as
 natural transformations
In-Reply-To: <CA+ixoL=VKs2yy2VrOUeWwWV7mFXY9ZOV5hoSdt3FHQOA18cx_A@mail.gmail.com>
References: <CA+ixoL=c22yAzzzvx=-sXO4h2V=LmKegJN_4PJuqaSJ-cg-qSw@mail.gmail.com>
 <20131114135911.GA31874@seas.upenn.edu>
 <CA+ixoL=VKs2yy2VrOUeWwWV7mFXY9ZOV5hoSdt3FHQOA18cx_A@mail.gmail.com>
Message-ID: <20131222202650.GA32404@seas.upenn.edu>

Hi Matt,

On Fri, Dec 13, 2013 at 03:25:03PM +0000, Matt R wrote:
> 
> Note that you can't always characterize a type class by a single
> > function like this.  For example, consider class Foo ... There is no way
> > to pick functors f and g such that a Foo dictionary is
> > equivalent to  f a -> g a.
> >
> 
> I was wondering why the following wouldn't do the trick?
> 
> sig :: Foo a => Either Int a -> Either a Int
> sig (Left n) = Left (bar n)
> sig (Right a) = Right (baz a)

You have encoded a Foo dictionary as an Either Int a -> Either a Int
function, but that is very different than saying that having a Foo
dictionary is *equivalent* to having an Either Int a -> Either a Int
function.  They are not equivalent; in particular, you could have a
function which sends Left 5 to Right 6, which does not correpond to
anything in Foo.  Put another way, if you try to write a Foo instance
given only some unknown function of type (Either Int a -> Either a
Int), you will find that you cannot do it.  So my point stands that it
is not always possible to *characterize* a type class as a natural
transformation.

> > This doesn't really make sense.  If a natural transformation
> > consists of a family of arrows which all live in Hask_T,
> 
> 
> In this case, I think the family of arrows lives in Hask -- we can
> reinterpret our Hask endofunctors as instead being functors from Hask_T ->
> Hask. Then there's no requirement on our constrained polymorphic functions
> to commute with sig.
> 
> In your example function f, the two functors would be the identify functor
> "Id" and a constant functor "K Foo", and naturality is just saying that,
> for any function g: A -> B that satisfies show == show . f, then:
> 
> f = f . g
> 
> Which is clearly true for f.

Hmm, yes, this seems plausible.

> Am I still barking up the wrong tree? Apologies if so, but it *feels* like
> there should be something here, with the intuition that:
> 
> Functions that don't "inspect" their values ==> you can substitute values
> without fundamentally affecting the action of the function ==> natural
> transformations between Hask endofunctors.
> 
> Functions that don't inspect their values other than through a particular
> interface T ==> you can substitute values without fundamentally affecting
> the action of the function, providing your substitution is invisible
> through the interface T ==> Natural transformations between functors Hask_T
> -> Hask.

Yes, makes sense I think.

-Brent

From byorgey at seas.upenn.edu  Sun Dec 22 20:35:24 2013
From: byorgey at seas.upenn.edu (Brent Yorgey)
Date: Sun, 22 Dec 2013 15:35:24 -0500
Subject: [Haskell-beginners] retreive a list of installed packages
In-Reply-To: <loom.20131222T153649-617@post.gmane.org>
References: <loom.20131222T153649-617@post.gmane.org>
Message-ID: <20131222203524.GB32404@seas.upenn.edu>

On Sun, Dec 22, 2013 at 02:38:53PM +0000, harry wrote:
> Is there any simple way for a program to retrieve a list of installed
> packages (such as ghc-pkg list returns), or would it be easier to execute
> phc-pkg as an external process and catch the output?

Try the hackage-db package:

  http://hackage.haskell.org/package/hackage%2Ddb

-Brent

From byorgey at seas.upenn.edu  Sun Dec 22 20:38:42 2013
From: byorgey at seas.upenn.edu (Brent Yorgey)
Date: Sun, 22 Dec 2013 15:38:42 -0500
Subject: [Haskell-beginners] Is Cons in the Haskell Module Library
In-Reply-To: <869634CA9D1B4FF2A8ED6BB20D4A013E@UserPC>
References: <869634CA9D1B4FF2A8ED6BB20D4A013E@UserPC>
Message-ID: <20131222203842.GC32404@seas.upenn.edu>

On Sun, Dec 22, 2013 at 12:23:42PM -0500, Patrick Lynch wrote:
> Good morning,
> I'm going through Graham Hutton's link on Category Theory [and yes I understand that you needn't study CT in order to use Haskell] and he uses Cons.
> I realize that Cons may be a synonym for ':'.
> But can someone tell me how to search the Haskell Library to find the module containing Cons?
> Thank you and Merry Christmas

Are you asking how to find the definition of (:) in Haskell? (It is
special built-in syntax.)  Or are you asking how to find out what
Graham Hutton means by 'Cons'?  In the latter case, you will have to
tell us exactly where in his notes to look, because out of context it
is impossible to tell.

-Brent

From vikraman.choudhury at gmail.com  Sun Dec 22 20:54:47 2013
From: vikraman.choudhury at gmail.com (Vikraman)
Date: Mon, 23 Dec 2013 02:24:47 +0530
Subject: [Haskell-beginners] Is Cons in the Haskell Module Library
In-Reply-To: <20131222203842.GC32404@seas.upenn.edu>
References: <869634CA9D1B4FF2A8ED6BB20D4A013E@UserPC>
 <20131222203842.GC32404@seas.upenn.edu>
Message-ID: <20131222205447.GA6620@felicia.cse.iitk.ac.in>

On Sun, Dec 22, 2013 at 03:38:42PM -0500, Brent Yorgey wrote:
> On Sun, Dec 22, 2013 at 12:23:42PM -0500, Patrick Lynch wrote:
> > Good morning,
> > I'm going through Graham Hutton's link on Category Theory [and yes I understand that you needn't study CT in order to use Haskell] and he uses Cons.
> > I realize that Cons may be a synonym for ':'.
> > But can someone tell me how to search the Haskell Library to find the module containing Cons?
> > Thank you and Merry Christmas
> 
> Are you asking how to find the definition of (:) in Haskell? (It is
> special built-in syntax.)  Or are you asking how to find out what
> Graham Hutton means by 'Cons'?  In the latter case, you will have to
> tell us exactly where in his notes to look, because out of context it
> is impossible to tell.
> 

Probably this one, page 4.

http://www.cs.nott.ac.uk/~gmh/cat2.pdf

-- 
Vikraman

From anguscomber at gmail.com  Mon Dec 23 13:55:12 2013
From: anguscomber at gmail.com (Angus Comber)
Date: Mon, 23 Dec 2013 13:55:12 +0000
Subject: [Haskell-beginners] Question on : usage
Message-ID: <CAAtGUhWbe-os+bEM3xNAc2PGO52xXE7g2PDjq0rXOOTKr+Kn0Q@mail.gmail.com>

I am playing with concatenating lists so I start with this:

testconcat :: [[a]] -> [a]
testconcat [[]] = []
testconcat [(x:xs)] = x : xs

Now, testconcat [[]] and testconcat [[1,2]] works

So now I want to try with a 2nd inner list so I do this:

testconcat :: [[a]] -> [a]
testconcat [[]] = []
testconcat [(x:xs)] = x : xs
testconcat [(x:xs), (y:ys)] = x : xs : y : ys

and I get load error:
    Couldn't match expected type `a' with actual type `[a]'
      `a' is a rigid type variable bound by
          the type signature for testconcat :: [[a]] -> [a]
          at prog_haskell.hs:218:15
    In the first argument of `(:)', namely `xs'
    In the second argument of `(:)', namely `xs : y : ys'
    In the expression: x : xs : y : ys


But this loads ok:
testconcat :: [[a]] -> [a]
testconcat [[]] = []
testconcat [(x:xs)] = x : xs
testconcat [(x:xs), (y:ys)] = x : xs

Even this line cannot be loaded:
testconcat [(x:xs), (y:ys)] = x : xs : []

    Couldn't match expected type `a' with actual type `[a]'
      `a' is a rigid type variable bound by
          the type signature for testconcat :: [[a]] -> [a]
          at prog_haskell.hs:218:15
    In the first argument of `(:)', namely `xs'
    In the second argument of `(:)', namely `xs : []'
    In the expression: x : xs : []
Failed, modules loaded: none.

if x : xs works why not x : xs : <something else> ???

Can someone please explain?
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From allbery.b at gmail.com  Mon Dec 23 14:03:46 2013
From: allbery.b at gmail.com (Brandon Allbery)
Date: Mon, 23 Dec 2013 09:03:46 -0500
Subject: [Haskell-beginners] Question on : usage
In-Reply-To: <CAAtGUhWbe-os+bEM3xNAc2PGO52xXE7g2PDjq0rXOOTKr+Kn0Q@mail.gmail.com>
References: <CAAtGUhWbe-os+bEM3xNAc2PGO52xXE7g2PDjq0rXOOTKr+Kn0Q@mail.gmail.com>
Message-ID: <CAKFCL4Xz-KyifWfy0Nd1u720ogiE+ZEXpMfE=Q5=ka+XHN6tGg@mail.gmail.com>

On Mon, Dec 23, 2013 at 8:55 AM, Angus Comber <anguscomber at gmail.com> wrote:

>     Couldn't match expected type `a' with actual type `[a]'
>       `a' is a rigid type variable bound by
>           the type signature for testconcat :: [[a]] -> [a]
>           at prog_haskell.hs:218:15
>     In the first argument of `(:)', namely `xs'
>     In the second argument of `(:)', namely `xs : []'
>     In the expression: x : xs : []
> Failed, modules loaded: none.
>
> if x : xs works why not x : xs : <something else> ???
>

x is an element.
xs is a list of those elements.
x : xs prepends a single element to a list.
x : xs : y would attempt to prepend a single element *and* a list to
something else --- but if you deconstructed a list to get x and xs, then x
and xs are not the same type (since xs's type is that of a list of x).

Perhaps the thing to understand is that in Haskell, a list is built up of
elements all of the same type using (:):

[x,y,z]   is the same as   x : y : z : []

(If you're familiar with Lisp, (:) is exactly cons and [] is nil.)

But because Haskell is strictly typed, a list must contain elements all the
same type. So you can't have y in that be a list of the same type as x, it
must be a value the same type as x.

Maybe you are looking for (++) instead? But note that that takes lists, not
items, so it would have to be ([x] ++ xs ++ ...).

-- 
brandon s allbery kf8nh                               sine nomine associates
allbery.b at gmail.com                                  ballbery at sinenomine.net
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net
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From akaberto at gmail.com  Mon Dec 23 14:05:54 2013
From: akaberto at gmail.com (akash g)
Date: Mon, 23 Dec 2013 19:35:54 +0530
Subject: [Haskell-beginners] Question on : usage
In-Reply-To: <CAAtGUhWbe-os+bEM3xNAc2PGO52xXE7g2PDjq0rXOOTKr+Kn0Q@mail.gmail.com>
References: <CAAtGUhWbe-os+bEM3xNAc2PGO52xXE7g2PDjq0rXOOTKr+Kn0Q@mail.gmail.com>
Message-ID: <CALiga_cyhMcJZNZ-rrQ_Y66Xk8wq0JrQHUaOVWPg5ABVsgt6ew@mail.gmail.com>

Because the type of cons (:) is a -> [a] -> [a].
Thus, when you do list : something else, you get a type mismatch.  You are
basically giving it [a] -> [a] -> [a].
You got yourself a type violation.



On Mon, Dec 23, 2013 at 7:25 PM, Angus Comber <anguscomber at gmail.com> wrote:

> I am playing with concatenating lists so I start with this:
>
> testconcat :: [[a]] -> [a]
> testconcat [[]] = []
> testconcat [(x:xs)] = x : xs
>
> Now, testconcat [[]] and testconcat [[1,2]] works
>
> So now I want to try with a 2nd inner list so I do this:
>
> testconcat :: [[a]] -> [a]
> testconcat [[]] = []
> testconcat [(x:xs)] = x : xs
> testconcat [(x:xs), (y:ys)] = x : xs : y : ys
>
> and I get load error:
>     Couldn't match expected type `a' with actual type `[a]'
>       `a' is a rigid type variable bound by
>           the type signature for testconcat :: [[a]] -> [a]
>           at prog_haskell.hs:218:15
>     In the first argument of `(:)', namely `xs'
>     In the second argument of `(:)', namely `xs : y : ys'
>     In the expression: x : xs : y : ys
>
>
> But this loads ok:
> testconcat :: [[a]] -> [a]
> testconcat [[]] = []
> testconcat [(x:xs)] = x : xs
> testconcat [(x:xs), (y:ys)] = x : xs
>
> Even this line cannot be loaded:
> testconcat [(x:xs), (y:ys)] = x : xs : []
>
>     Couldn't match expected type `a' with actual type `[a]'
>       `a' is a rigid type variable bound by
>           the type signature for testconcat :: [[a]] -> [a]
>           at prog_haskell.hs:218:15
>     In the first argument of `(:)', namely `xs'
>     In the second argument of `(:)', namely `xs : []'
>     In the expression: x : xs : []
> Failed, modules loaded: none.
>
> if x : xs works why not x : xs : <something else> ???
>
> Can someone please explain?
>
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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From daniel.trstenjak at gmail.com  Mon Dec 23 14:11:08 2013
From: daniel.trstenjak at gmail.com (Daniel Trstenjak)
Date: Mon, 23 Dec 2013 15:11:08 +0100
Subject: [Haskell-beginners] Question on : usage
In-Reply-To: <CAAtGUhWbe-os+bEM3xNAc2PGO52xXE7g2PDjq0rXOOTKr+Kn0Q@mail.gmail.com>
References: <CAAtGUhWbe-os+bEM3xNAc2PGO52xXE7g2PDjq0rXOOTKr+Kn0Q@mail.gmail.com>
Message-ID: <20131223141108.GA10571@machine>


Hi Angus,

> testconcat [(x:xs), (y:ys)] = x : xs : y : ys

When you're replacing the x, xs, y, and ys with types you're getting:

   a : [a] : a : [a]

The type of (:) is:

   a -> [a] -> [a]

Can you see the problem? Hint, the problem is the (:) in the middle.


Greetings,
Daniel

From michael at orlitzky.com  Mon Dec 23 14:12:25 2013
From: michael at orlitzky.com (Michael Orlitzky)
Date: Mon, 23 Dec 2013 09:12:25 -0500
Subject: [Haskell-beginners] Question on : usage
In-Reply-To: <CAAtGUhWbe-os+bEM3xNAc2PGO52xXE7g2PDjq0rXOOTKr+Kn0Q@mail.gmail.com>
References: <CAAtGUhWbe-os+bEM3xNAc2PGO52xXE7g2PDjq0rXOOTKr+Kn0Q@mail.gmail.com>
Message-ID: <52B844C9.4090705@orlitzky.com>

On 12/23/2013 08:55 AM, Angus Comber wrote:
> I am playing with concatenating lists so I start with this:
> 
> testconcat :: [[a]] -> [a]
> testconcat [[]] = []
> testconcat [(x:xs)] = x : xs
> 
> Now, testconcat [[]] and testconcat [[1,2]] works
> 
> So now I want to try with a 2nd inner list so I do this:
> 
> testconcat :: [[a]] -> [a]
> testconcat [[]] = []
> testconcat [(x:xs)] = x : xs
> testconcat [(x:xs), (y:ys)] = x : xs : y : ys
> 
> and I get load error:
>     Couldn't match expected type `a' with actual type `[a]'
>       `a' is a rigid type variable bound by
>           the type signature for testconcat :: [[a]] -> [a]
>           at prog_haskell.hs:218:15
>     In the first argument of `(:)', namely `xs'
>     In the second argument of `(:)', namely `xs : y : ys'
>     In the expression: x : xs : y : ys
> 

The colon operator (:) takes a single element on the left, and a list on
the right. In,

  testconcat [(x:xs), (y:ys)] = x : xs : y : ys

you've got lists on both the left and the right. This would work:

  testconcat [(x:xs), (y:ys)] = x : ( y : (xs ++ ys) )

(note: not the same function as you wanted!) since it keeps all of the
single-elements on the left-hand side of (:). You're going to need to
use (++) in at least one place, though, since you need to combine the
lists 'xs' and 'ys' somehow. The function you really want is,

  testconcat [(x:xs), (y:ys)] = (x:xs) ++ (y:ys)

but of course this is just,

  testconcat [l1, l2] = l1 ++ l2


From anguscomber at gmail.com  Mon Dec 23 14:57:35 2013
From: anguscomber at gmail.com (Angus Comber)
Date: Mon, 23 Dec 2013 14:57:35 +0000
Subject: [Haskell-beginners] Question on (x:xs) form
Message-ID: <CAAtGUhUA3Mf0GeX0mcMamtDPdp7OVS3pwKBPjyk2inS4QcJ8zA@mail.gmail.com>

Eg for a definition of reverse:

reverse' :: [a] -> [a]
reverse' [] = []
reverse' (x:xs) = reverse' xs ++ [x]

In the last line of the definition, x is an element in the list (the first
element) and xs represents the remainder of the list.

so if list was [1,2,3] then x is 1 and xs is [2,3]

Why are the brackets required?  And what do they signify?

Eg reverse' x:xs = reverse' xs ++ [x] results in a parse error.
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From allbery.b at gmail.com  Mon Dec 23 15:03:26 2013
From: allbery.b at gmail.com (Brandon Allbery)
Date: Mon, 23 Dec 2013 10:03:26 -0500
Subject: [Haskell-beginners] Question on (x:xs) form
In-Reply-To: <CAAtGUhUA3Mf0GeX0mcMamtDPdp7OVS3pwKBPjyk2inS4QcJ8zA@mail.gmail.com>
References: <CAAtGUhUA3Mf0GeX0mcMamtDPdp7OVS3pwKBPjyk2inS4QcJ8zA@mail.gmail.com>
Message-ID: <CAKFCL4Vy3tiAaMXge3HZMP+NmNSU7mjQuWXasEh81ffQUOmA0g@mail.gmail.com>

On Mon, Dec 23, 2013 at 9:57 AM, Angus Comber <anguscomber at gmail.com> wrote:

> Why are the brackets required?  And what do they signify?
> Eg reverse' x:xs = reverse' xs ++ [x] results in a parse error.
>

If you leave them off then it's parsed as three parameters instead of a
pattern as a single parameter. But that also leads to a parse error since
you can't use a bare operator that way. Which is "weird", but you can get
into inconsistent parses if you try to guess that the parentheses are
needed: should it be `(x:xs)` a pattern, or should it be `x (:) xs` 3
patterns with an infix constructor as the second?

-- 
brandon s allbery kf8nh                               sine nomine associates
allbery.b at gmail.com                                  ballbery at sinenomine.net
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net
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From ky3 at atamo.com  Mon Dec 23 15:56:24 2013
From: ky3 at atamo.com (Kim-Ee Yeoh)
Date: Mon, 23 Dec 2013 22:56:24 +0700
Subject: [Haskell-beginners] Question on (x:xs) form
In-Reply-To: <CAAtGUhUA3Mf0GeX0mcMamtDPdp7OVS3pwKBPjyk2inS4QcJ8zA@mail.gmail.com>
References: <CAAtGUhUA3Mf0GeX0mcMamtDPdp7OVS3pwKBPjyk2inS4QcJ8zA@mail.gmail.com>
Message-ID: <CAPY+ZdSXJGBGNCOd+ZVzWP=qg4G4w3u9xhGpiOU7zMve9PU8hA@mail.gmail.com>

On Mon, Dec 23, 2013 at 9:57 PM, Angus Comber <anguscomber at gmail.com> wrote:

> Why are the brackets required?  And what do they signify?
>
> Eg reverse' x:xs = reverse' xs ++ [x] results in a parse error.
>

So a number of Haskell-specific themes are relevant here, especially if you
come from a Lisp background:

* types (but you knew that already!)
* pattern-matching & exhaustivity of matches
* operator infix notation
* associativity precedence
* special notation for lists

It's a good idea to watch out for all of the above when learning the
language. It helps to have some google-able names when the situation is
ripe for drilling deep into these topics.

To elaborate a bit,

Special List Notation: lists use (:) and [x]. But this syntax is baked
specially into the language definition! If you define your own list, it'll
typically look like
   data List a = Nil | Cons a (List a)   -- note the parens!

The alternative GADT-ish style may make this clearer:
   data List a  where
      Nil :: List a
      Cons :: a -> List a -> List a

Nil and Cons are data constructor *functions*, and because and only because
they are so, do they get to have Capitalized Names. <------- this is
another big WTF that trips up many, many learners. Especially with code
like:
   newtype X a = X a   -- whaaaa????? (It's ok, you'll get it soon enough.)

Back to reverse'. With our user-defined List a, reverse' will look like
   reverse' Nil =
   reverse' (Cons x xs) = ...  -- again note the parens!

(There is however, *NO* difference in the semantics. The code just looks
different but the compiler doesn't care.)

Note how the pattern-matching includes every single case of the sum-type;
here both of them: Nil and Cons. This is Generally A Good Thing!

-- Kim-Ee
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From denisalbuquerque at gmail.com  Mon Dec 23 18:55:35 2013
From: denisalbuquerque at gmail.com (Denis Albuquerque)
Date: Mon, 23 Dec 2013 16:55:35 -0200
Subject: [Haskell-beginners] Question on (x:xs) form
In-Reply-To: <CAAtGUhUA3Mf0GeX0mcMamtDPdp7OVS3pwKBPjyk2inS4QcJ8zA@mail.gmail.com>
References: <CAAtGUhUA3Mf0GeX0mcMamtDPdp7OVS3pwKBPjyk2inS4QcJ8zA@mail.gmail.com>
Message-ID: <CAGFjeK4x5RYMNQcHTERfd-qHRPST9N0VkHqMGh4ReFgFWswtDg@mail.gmail.com>

Hi Angus,

you need to put the parentheses around the pattern x:xs because the
application reverse' has priority over (:) , so the statement is the
same as

(reverse' x):xs = reverse' xs ++ [x]

and results the error.

-- Denis.

On Mon, Dec 23, 2013 at 12:57 PM, Angus Comber <anguscomber at gmail.com> wrote:
> Eg for a definition of reverse:
>
> reverse' :: [a] -> [a]
> reverse' [] = []
> reverse' (x:xs) = reverse' xs ++ [x]
>
> In the last line of the definition, x is an element in the list (the first
> element) and xs represents the remainder of the list.
>
> so if list was [1,2,3] then x is 1 and xs is [2,3]
>
> Why are the brackets required?  And what do they signify?
>
> Eg reverse' x:xs = reverse' xs ++ [x] results in a parse error.
>
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>

From miroslav.karpis at gmail.com  Mon Dec 23 21:42:47 2013
From: miroslav.karpis at gmail.com (Miro Karpis)
Date: Mon, 23 Dec 2013 22:42:47 +0100
Subject: [Haskell-beginners] breaking code to several lines
Message-ID: <CAJnnbxEFJopPF-3s5joa9=x7USmZnHRO+t73u+kkb05OwefyxQ@mail.gmail.com>

Hi please,... I have one sql insert statement which is too long to be on
one line. Is there a way that I can break it several lines? Or does it have
to be everything in one line?

here is the query:
    execute_ conn "INSERT INTO ttableXY
(column1, column2, column3, column4, column5, column6, column7) VALUES
('var1', 'var2', 'var3', 'var4', 'var5', 'var6', 'var7')"

Thanks,
Miro
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From allbery.b at gmail.com  Mon Dec 23 21:47:12 2013
From: allbery.b at gmail.com (Brandon Allbery)
Date: Mon, 23 Dec 2013 16:47:12 -0500
Subject: [Haskell-beginners] breaking code to several lines
In-Reply-To: <CAJnnbxEFJopPF-3s5joa9=x7USmZnHRO+t73u+kkb05OwefyxQ@mail.gmail.com>
References: <CAJnnbxEFJopPF-3s5joa9=x7USmZnHRO+t73u+kkb05OwefyxQ@mail.gmail.com>
Message-ID: <CAKFCL4Vws_y-g10m4KYN6fEx4zqV9dtQk7+_abW1857m5PghBQ@mail.gmail.com>

On Mon, Dec 23, 2013 at 4:42 PM, Miro Karpis <miroslav.karpis at gmail.com>wrote:

> Hi please,... I have one sql insert statement which is too long to be on
> one line. Is there a way that I can break it several lines? Or does it have
> to be everything in one line?
>

See "string gaps" in
http://www.haskell.org/onlinereport/haskell2010/haskellch2.html#x7-200002.6

-- 
brandon s allbery kf8nh                               sine nomine associates
allbery.b at gmail.com                                  ballbery at sinenomine.net
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net
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From toad3k at gmail.com  Mon Dec 23 21:57:48 2013
From: toad3k at gmail.com (David McBride)
Date: Mon, 23 Dec 2013 16:57:48 -0500
Subject: [Haskell-beginners] breaking code to several lines
In-Reply-To: <CAJnnbxEFJopPF-3s5joa9=x7USmZnHRO+t73u+kkb05OwefyxQ@mail.gmail.com>
References: <CAJnnbxEFJopPF-3s5joa9=x7USmZnHRO+t73u+kkb05OwefyxQ@mail.gmail.com>
Message-ID: <CAN+Tr40N91c3a7P0y-zz6ew=BFJROC2TWStzpMXMskhYn=LQ3g@mail.gmail.com>

Another option is a string quasiquoter.  There are several options
available, non interpolating ones ones such as string-qq or string-quote,
as well as ones that allow you to interpolate variables, like
interpolatedstring-qq.


On Mon, Dec 23, 2013 at 4:42 PM, Miro Karpis <miroslav.karpis at gmail.com>wrote:

> Hi please,... I have one sql insert statement which is too long to be on
> one line. Is there a way that I can break it several lines? Or does it have
> to be everything in one line?
>
> here is the query:
>     execute_ conn "INSERT INTO ttableXY
> (column1, column2, column3, column4, column5, column6, column7) VALUES
> ('var1', 'var2', 'var3', 'var4', 'var5', 'var6', 'var7')"
>
> Thanks,
> Miro
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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From miroslav.karpis at gmail.com  Mon Dec 23 22:05:13 2013
From: miroslav.karpis at gmail.com (Miro Karpis)
Date: Mon, 23 Dec 2013 23:05:13 +0100
Subject: [Haskell-beginners] breaking code to several lines
In-Reply-To: <CAN+Tr40N91c3a7P0y-zz6ew=BFJROC2TWStzpMXMskhYn=LQ3g@mail.gmail.com>
References: <CAJnnbxEFJopPF-3s5joa9=x7USmZnHRO+t73u+kkb05OwefyxQ@mail.gmail.com>
 <CAN+Tr40N91c3a7P0y-zz6ew=BFJROC2TWStzpMXMskhYn=LQ3g@mail.gmail.com>
Message-ID: <CAJnnbxHn+0-_6KM=bgPhAy5gO560OSb39TQWWeBo_q8DM8EZxg@mail.gmail.com>

thank you very much

m.


On Mon, Dec 23, 2013 at 10:57 PM, David McBride <toad3k at gmail.com> wrote:

> Another option is a string quasiquoter.  There are several options
> available, non interpolating ones ones such as string-qq or string-quote,
> as well as ones that allow you to interpolate variables, like
> interpolatedstring-qq.
>
>
> On Mon, Dec 23, 2013 at 4:42 PM, Miro Karpis <miroslav.karpis at gmail.com>wrote:
>
>> Hi please,... I have one sql insert statement which is too long to be on
>> one line. Is there a way that I can break it several lines? Or does it have
>> to be everything in one line?
>>
>> here is the query:
>>     execute_ conn "INSERT INTO ttableXY
>> (column1, column2, column3, column4, column5, column6, column7) VALUES
>> ('var1', 'var2', 'var3', 'var4', 'var5', 'var6', 'var7')"
>>
>> Thanks,
>> Miro
>>
>> _______________________________________________
>> Beginners mailing list
>> Beginners at haskell.org
>> http://www.haskell.org/mailman/listinfo/beginners
>>
>>
>
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From miroslav.karpis at gmail.com  Tue Dec 24 00:37:45 2013
From: miroslav.karpis at gmail.com (Miro Karpis)
Date: Tue, 24 Dec 2013 01:37:45 +0100
Subject: [Haskell-beginners] Database.SQLite.Simple: Select query with more
	than 10 elements tuple
Message-ID: <CAJnnbxGEn=XFw79ri82PSfN-W0GYKSgg=MZFhgq_d9oZNMoQJw@mail.gmail.com>

Hi, please ... I need help with following:

I have a table with 11 columns. I would like to create a query where in
return I should get values of all columns. Problem is that when I try with
10 elements everything works OK. With 11 I will get compile error.

I found in the Database.SQLite.Simple documentation following:
A collection type that can be converted from a sequence of fields.
Instances are provided for tuples up to 10 elements and lists of any length.

So is it possible to select more than 10 columns in one query? It must be
right?


working code:
-------------------------
queryX :: Query
queryX = "SELECT el1, el2, el3, el4, el5, el6, el7, el8, el9, el10 FROM
tableX"

saveBtceTickerData :: IO ()
saveBtceTickerData = do
    conn <- open "../mydb.sqlite"
    r <- query_ conn queryX :: IO [(Double, Int, Double, Double, Double,
Double, Double, Double, Double, Double)]
    mapM_ print r
    close conn
    putStrLn "done"


non-working code:
-------------------------
someQuery :: Query
someQuery = "SELECT el1, el2, el3, el4, el5, el6, el7, el8, el9, el10, el11
FROM tableX"

saveBtceTickerData :: IO ()
saveBtceTickerData = do
    conn <- open "../mydb.sqlite"
    r <- query_ conn queryX :: IO [(Double, Int, Double, Double, Double,
Double, Double, Double, Double, Double, Double)]
    mapM_ print r
    close conn
    putStrLn "done"

------
Error output:

No instance for (FromRow

                       (Double,

                        Int,

                        Double,

                        Double,

                        Double,

                        Double,

                        Double,

                        Double,

                        Double,

                        Double,

                        Double))

      arising from a use of `query_'

    Possible fix:

      add an instance declaration for

      (FromRow

         (Double,

          Int,

          Double,

          Double,

          Double,

          Double,

          Double,

          Double,

          Double,

          Double,

          Double))


thanks,
m.
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From toad3k at gmail.com  Tue Dec 24 01:16:07 2013
From: toad3k at gmail.com (David McBride)
Date: Mon, 23 Dec 2013 20:16:07 -0500
Subject: [Haskell-beginners] Database.SQLite.Simple: Select query with
 more than 10 elements tuple
In-Reply-To: <CAJnnbxGEn=XFw79ri82PSfN-W0GYKSgg=MZFhgq_d9oZNMoQJw@mail.gmail.com>
References: <CAJnnbxGEn=XFw79ri82PSfN-W0GYKSgg=MZFhgq_d9oZNMoQJw@mail.gmail.com>
Message-ID: <CAN+Tr4192LufQOm5f0iAAOC1yWN_GKhgSmphi16F7EBJyF7RSg@mail.gmail.com>

You can use the :. operator to separate different types.  You can string
them together for as long as you want.  WIth ScopedTypeVariables extension
enabled you can type them in an anon function like so.

forM_ res $ \((Only (x :: Int)) :. (Only (y :: Int)) ) -> do
    print (show x) ++ (show y)

You can also create your own 11+ item datatype and create a fromRow
instance for it, which would serve the same purpose.



On Mon, Dec 23, 2013 at 7:37 PM, Miro Karpis <miroslav.karpis at gmail.com>wrote:

> Hi, please ... I need help with following:
>
> I have a table with 11 columns. I would like to create a query where in
> return I should get values of all columns. Problem is that when I try with
> 10 elements everything works OK. With 11 I will get compile error.
>
> I found in the Database.SQLite.Simple documentation following:
> A collection type that can be converted from a sequence of fields.
> Instances are provided for tuples up to 10 elements and lists of any length.
>
> So is it possible to select more than 10 columns in one query? It must be
> right?
>
>
> working code:
> -------------------------
> queryX :: Query
> queryX = "SELECT el1, el2, el3, el4, el5, el6, el7, el8, el9, el10 FROM
> tableX"
>
> saveBtceTickerData :: IO ()
> saveBtceTickerData = do
>     conn <- open "../mydb.sqlite"
>     r <- query_ conn queryX :: IO [(Double, Int, Double, Double, Double,
> Double, Double, Double, Double, Double)]
>     mapM_ print r
>     close conn
>     putStrLn "done"
>
>
> non-working code:
> -------------------------
> someQuery :: Query
> someQuery = "SELECT el1, el2, el3, el4, el5, el6, el7, el8, el9, el10,
> el11 FROM tableX"
>
> saveBtceTickerData :: IO ()
> saveBtceTickerData = do
>     conn <- open "../mydb.sqlite"
>     r <- query_ conn queryX :: IO [(Double, Int, Double, Double, Double,
> Double, Double, Double, Double, Double, Double)]
>     mapM_ print r
>     close conn
>     putStrLn "done"
>
> ------
> Error output:
>
> No instance for (FromRow
>
>                        (Double,
>
>                         Int,
>
>                         Double,
>
>                         Double,
>
>                         Double,
>
>                         Double,
>
>                         Double,
>
>                         Double,
>
>                         Double,
>
>                         Double,
>
>                         Double))
>
>       arising from a use of `query_'
>
>     Possible fix:
>
>       add an instance declaration for
>
>       (FromRow
>
>          (Double,
>
>           Int,
>
>           Double,
>
>           Double,
>
>           Double,
>
>           Double,
>
>           Double,
>
>           Double,
>
>           Double,
>
>           Double,
>
>           Double))
>
>
> thanks,
> m.
>
>
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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From anguscomber at gmail.com  Tue Dec 24 13:19:42 2013
From: anguscomber at gmail.com (Angus Comber)
Date: Tue, 24 Dec 2013 13:19:42 +0000
Subject: [Haskell-beginners] Trying to understand the foldl type?
Message-ID: <CAAtGUhWfmF7JQvSh270xN9KbHVa2fxCe6f=WxYxTchqu79fPkg@mail.gmail.com>

The type is:

foldl :: (a -> b -> a) -> a -> [b] -> a

Eg I might do something like this:

foldl (+) 0 [1..10]

so taking (a -> b -> a)

leftmost a is (+)
b is 0
right a is what?  The first value in the list?

Then -> ?

[b] ?  Is this like the temporary recursion calculation?

final -> a is the result?
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From bob at redivi.com  Tue Dec 24 13:47:23 2013
From: bob at redivi.com (Bob Ippolito)
Date: Tue, 24 Dec 2013 05:47:23 -0800
Subject: [Haskell-beginners] Trying to understand the foldl type?
In-Reply-To: <CAAtGUhWfmF7JQvSh270xN9KbHVa2fxCe6f=WxYxTchqu79fPkg@mail.gmail.com>
References: <CAAtGUhWfmF7JQvSh270xN9KbHVa2fxCe6f=WxYxTchqu79fPkg@mail.gmail.com>
Message-ID: <CACwMPm-q=kK3oAxT611uR5wxCakUUbvrB8nLn4LeFzMLRNCeXQ@mail.gmail.com>

Given foldl (+) 0 [1..10]
(+) is (a -> b -> a)
0 is a
[1..10] is [b]
and the final a is the result of the expression.

On Tuesday, December 24, 2013, Angus Comber wrote:

> The type is:
>
> foldl :: (a -> b -> a) -> a -> [b] -> a
>
> Eg I might do something like this:
>
> foldl (+) 0 [1..10]
>
> so taking (a -> b -> a)
>
> leftmost a is (+)
> b is 0
> right a is what?  The first value in the list?
>
> Then -> ?
>
> [b] ?  Is this like the temporary recursion calculation?
>
> final -> a is the result?
>
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From ky3 at atamo.com  Tue Dec 24 15:21:52 2013
From: ky3 at atamo.com (Kim-Ee Yeoh)
Date: Tue, 24 Dec 2013 22:21:52 +0700
Subject: [Haskell-beginners] Trying to understand the foldl type?
In-Reply-To: <CAAtGUhWfmF7JQvSh270xN9KbHVa2fxCe6f=WxYxTchqu79fPkg@mail.gmail.com>
References: <CAAtGUhWfmF7JQvSh270xN9KbHVa2fxCe6f=WxYxTchqu79fPkg@mail.gmail.com>
Message-ID: <CAPY+ZdSddOwVmxdqLsPaF62V47aXtB=rEFByxK0HaT+Ux4sgLQ@mail.gmail.com>

On Tue, Dec 24, 2013 at 8:19 PM, Angus Comber <anguscomber at gmail.com> wrote:

> foldl :: (a -> b -> a) -> a -> [b] -> a
>
> Eg I might do something like this:
>
> foldl (+) 0 [1..10]
>

Try the following in ghci to see if you get an idea of what's going on:

:t foldl

:t foldl (+)

:t foldl (+) 0

:t foldl (+) 0 [1..10]

-- Kim-Ee
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From guthrie at mum.edu  Wed Dec 25 17:38:50 2013
From: guthrie at mum.edu (Gregory Guthrie)
Date: Wed, 25 Dec 2013 11:38:50 -0600
Subject: [Haskell-beginners] OMG - Cabal again...
Message-ID: <08EF9DA445C4B5439C4733E1F35705BA032C28CC8D97@MAIL.cs.mum.edu>

YACP - Yet another cabal problem...

Trying to install criterion, which fails for test-framework, which fails for regex, which fails for mtl, which reports that it is fine and installed!
Is there any simple recipe to restart the libraries for cabal (on windows)?

C:\Users\guthrie>cabal install criterion
Resolving dependencies...
In order, the following will be installed:
...
criterion-0.8.0.0 depends on test-framework-0.8.0.3 which failed to install.
hastache-0.5.1 failed during the building phase. The exception was: ExitFailure 1
math-functions-0.1.4.0 failed during the building phase. The exception was: ExitFailure 1
monad-par-0.3.4.6 depends on test-framework-0.8.0.3 which failed to install.
monad-par-extras-0.3.3 failed during the building phase. The exception was: ExitFailure 1
mwc-random-0.13.1.0 failed during the building phase. The exception was: ExitFailure 1
statistics-0.10.5.1 depends on test-framework-0.8.0.3 which failed to install.
test-framework-0.8.0.3 failed during the configure step. The exception was: ExitFailure 1
test-framework-hunit-0.3.0.1 depends on test-framework-0.8.0.3 which failed to install.
vector-algorithms-0.6.0.1 depends on mwc-random-0.13.1.0 which failed to install.
vector-binary-instances-0.2.1.0 failed during the building phase. The exception was: ExitFailure 1

C:\Users\guthrie>cabal install test-framework
Resolving dependencies...
Configuring test-framework-0.8.0.3...
cabal: The following installed packages are broken because other packages they
depend on are missing. These broken packages must be rebuilt before they can be used.
package regex-base-0.93.2 is broken due to missing package
mtl-2.1.2-5337caef659244e51e2f5fb2e944d97f
Failed to install test-framework-0.8.0.3
cabal: Error: some packages failed to install:
test-framework-0.8.0.3 failed during the configure step. The exception was: ExitFailure 1

C:\Users\guthrie>cabal install mtl
Resolving dependencies...
All the requested packages are already installed: mtl-2.1.2
Use --reinstall if you want to reinstall anyway.
-------------------------------------------
Dr. Gregory Guthrie

Computer Science Department
Dean, and Professor of Computer Science
School of Computer Science & Mathematics
Maharishi University of Management
------------------------------------------- 



From voldermort at hotmail.com  Sun Dec 29 12:17:20 2013
From: voldermort at hotmail.com (harry)
Date: Sun, 29 Dec 2013 12:17:20 +0000 (UTC)
Subject: [Haskell-beginners] anonymous arguments
Message-ID: <loom.20131229T130029-204@post.gmane.org>

Is there any reason not to include Scala-like anonymous arguments in
Haskell? For example, I would like to write
  map (\x -> foo x 3)
as
  map (foo _ 3)

The named argument in this and similar cases adds nothing but visual and
namespace clutter.


From tmorris at tmorris.net  Sun Dec 29 12:37:51 2013
From: tmorris at tmorris.net (Tony Morris)
Date: Sun, 29 Dec 2013 22:37:51 +1000
Subject: [Haskell-beginners] anonymous arguments
In-Reply-To: <loom.20131229T130029-204@post.gmane.org>
References: <loom.20131229T130029-204@post.gmane.org>
Message-ID: <CAJf6UsjxzCO5z3q5Mbn3wJ2+d0Af1MzjTn85cPAewt6ouf+zCg@mail.gmail.com>

(`foo` 3)

Scala is very limited when it comes to this point free code.
On 29/12/2013 10:17 PM, "harry" <voldermort at hotmail.com> wrote:

> Is there any reason not to include Scala-like anonymous arguments in
> Haskell? For example, I would like to write
>   map (\x -> foo x 3)
> as
>   map (foo _ 3)
>
> The named argument in this and similar cases adds nothing but visual and
> namespace clutter.
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
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From voldermort at hotmail.com  Sun Dec 29 12:47:48 2013
From: voldermort at hotmail.com (harry)
Date: Sun, 29 Dec 2013 12:47:48 +0000 (UTC)
Subject: [Haskell-beginners] anonymous arguments
References: <loom.20131229T130029-204@post.gmane.org>
 <CAJf6UsjxzCO5z3q5Mbn3wJ2+d0Af1MzjTn85cPAewt6ouf+zCg@mail.gmail.com>
Message-ID: <loom.20131229T133944-81@post.gmane.org>

Tony Morris <tmorris <at> tmorris.net> writes:
> 
> 
> (`foo` 3)
> Scala is very limited when it comes to this point free code. 
>
> On 29/12/2013 10:17 PM, "harry" <voldermort <at> hotmail.com> wrote:
>
> Is there any reason not to include Scala-like anonymous arguments in
> Haskell? For example, I would like to write
> ? map (\x -> foo x 3)
> as
> ? map (foo _ 3)
> The named argument in this and similar cases adds nothing but visual and
> namespace clutter.

How about a slightly more complex example?

  map (\x -> foo 4 'f' (bar x) 5 'j')

There comes a point where point-free notation becomes unreadable.


From twanvl at gmail.com  Sun Dec 29 13:24:13 2013
From: twanvl at gmail.com (Twan van Laarhoven)
Date: Sun, 29 Dec 2013 14:24:13 +0100
Subject: [Haskell-beginners] anonymous arguments
In-Reply-To: <loom.20131229T133944-81@post.gmane.org>
References: <loom.20131229T130029-204@post.gmane.org>
 <CAJf6UsjxzCO5z3q5Mbn3wJ2+d0Af1MzjTn85cPAewt6ouf+zCg@mail.gmail.com>
 <loom.20131229T133944-81@post.gmane.org>
Message-ID: <52C0227D.2050108@gmail.com>

On 2013-12-29 13:47, harry wrote:
> Tony Morris <tmorris <at> tmorris.net> writes:
>>
>>
>> (`foo` 3)
>> Scala is very limited when it comes to this point free code.
>>
>> On 29/12/2013 10:17 PM, "harry" <voldermort <at> hotmail.com> wrote:
>>
>> Is there any reason not to include Scala-like anonymous arguments in
>> Haskell? For example, I would like to write
>>    map (\x -> foo x 3)
>> as
>>    map (foo _ 3)
>> The named argument in this and similar cases adds nothing but visual and
>> namespace clutter.
>
> How about a slightly more complex example?
>
>    map (\x -> foo 4 'f' (bar x) 5 'j')
>
> There comes a point where point-free notation becomes unreadable.

If you write

     map (foo 4 'f' (bar _) 5 'j')

How would the compiler know whether you meant

     map (\x -> foo 4 'f' (bar x) 5 'j')

or

     map (foo 4 'f' (\x -> bar x) 5 'j')

?

Lambda's make it explicit where the variable is bound, which is a good thing, IMO.


Twan

From voldermort at hotmail.com  Sun Dec 29 13:39:36 2013
From: voldermort at hotmail.com (harry)
Date: Sun, 29 Dec 2013 13:39:36 +0000 (UTC)
Subject: [Haskell-beginners] anonymous arguments
References: <loom.20131229T130029-204@post.gmane.org>
 <CAJf6UsjxzCO5z3q5Mbn3wJ2+d0Af1MzjTn85cPAewt6ouf+zCg@mail.gmail.com>
 <loom.20131229T133944-81@post.gmane.org> <52C0227D.2050108@gmail.com>
Message-ID: <loom.20131229T143647-853@post.gmane.org>

Twan van Laarhoven <twanvl <at> gmail.com> writes:

> If you write
> 
>      map (foo 4 'f' (bar _) 5 'j')
> 
> How would the compiler know whether you meant
> 
>      map (\x -> foo 4 'f' (bar x) 5 'j')
> or
>      map (foo 4 'f' (\x -> bar x) 5 'j')
> ?

Interesting question, what does Scala do for this? I guess there would be a
rule of always binding to the outermost or innermost scope.





From toad3k at gmail.com  Sun Dec 29 21:27:08 2013
From: toad3k at gmail.com (David McBride)
Date: Sun, 29 Dec 2013 16:27:08 -0500
Subject: [Haskell-beginners] anonymous arguments
In-Reply-To: <loom.20131229T143647-853@post.gmane.org>
References: <loom.20131229T130029-204@post.gmane.org>
 <CAJf6UsjxzCO5z3q5Mbn3wJ2+d0Af1MzjTn85cPAewt6ouf+zCg@mail.gmail.com>
 <loom.20131229T133944-81@post.gmane.org>
 <52C0227D.2050108@gmail.com>
 <loom.20131229T143647-853@post.gmane.org>
Message-ID: <CAN+Tr41wkq5xte=TU26DPcsjMpWoKaO9M2-y-suYbbftkuvLig@mail.gmail.com>

I've seen the question asked on stackoverflow before.  It will be a very
subtle bug that scala does not catch for you.  You just have to have the
discpline not to nest multiple anonymous functions with underscore
arguments.  There's no way for the compiler to disallow it because it
cannot tell a mistake from something that is intentional.


On Sun, Dec 29, 2013 at 8:39 AM, harry <voldermort at hotmail.com> wrote:

> Twan van Laarhoven <twanvl <at> gmail.com> writes:
>
> > If you write
> >
> >      map (foo 4 'f' (bar _) 5 'j')
> >
> > How would the compiler know whether you meant
> >
> >      map (\x -> foo 4 'f' (bar x) 5 'j')
> > or
> >      map (foo 4 'f' (\x -> bar x) 5 'j')
> > ?
>
> Interesting question, what does Scala do for this? I guess there would be a
> rule of always binding to the outermost or innermost scope.
>
>
>
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
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From miroslav.karpis at gmail.com  Mon Dec 30 23:42:26 2013
From: miroslav.karpis at gmail.com (Miro Karpis)
Date: Tue, 31 Dec 2013 00:42:26 +0100
Subject: [Haskell-beginners] foldM with tuple and maybe
Message-ID: <CAJnnbxHfFJm+oedbToq0gXb7OxzFR+gPUPfnG7rETeupgbPcBg@mail.gmail.com>

Hi, please can you help me with following?

I have a following function:
f1 :: (String, String) -> IO (Maybe String)

which I would like to apply to a list of tuples.I have defined the function
like this, but that gives me error (below):

f2 :: [(String, String)] -> IO (Maybe String)
f2 x = foldM f1 0 x


error:
Couldn't match expected type `IO (Maybe String)'  with actual type `[b0] ->
m0 (String, String)' In the return type of a call of `foldM'

thanks,
m.
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From toad3k at gmail.com  Tue Dec 31 00:01:44 2013
From: toad3k at gmail.com (David McBride)
Date: Mon, 30 Dec 2013 19:01:44 -0500
Subject: [Haskell-beginners] foldM with tuple and maybe
In-Reply-To: <CAJnnbxHfFJm+oedbToq0gXb7OxzFR+gPUPfnG7rETeupgbPcBg@mail.gmail.com>
References: <CAJnnbxHfFJm+oedbToq0gXb7OxzFR+gPUPfnG7rETeupgbPcBg@mail.gmail.com>
Message-ID: <CAN+Tr41SFEmcbwRSeatPuNyvZ0k-Z=Bto_6MNRU8KHtj_-OqiA@mail.gmail.com>

You have a foldM function which takes a " a -> b -> m a " as a first
argument.  But you are passing it f1 which has a type (a, b) -> m a.

Unfortunately  I'm not sure what you were trying to do.  The function
you have just doesn't fit. :(

Maybe you intended to have f1 :: String -> (String, String) -> IO
String, and then go

:t foldM f1 "" x
foldM f1 "" [("a","b"),("c","d")] :: IO String


?

On Mon, Dec 30, 2013 at 6:42 PM, Miro Karpis <miroslav.karpis at gmail.com> wrote:
> Hi, please can you help me with following?
>
> I have a following function:
> f1 :: (String, String) -> IO (Maybe String)
>
> which I would like to apply to a list of tuples.I have defined the function
> like this, but that gives me error (below):
>
> f2 :: [(String, String)] -> IO (Maybe String)
> f2 x = foldM f1 0 x
>
>
> error:
> Couldn't match expected type `IO (Maybe String)'  with actual type `[b0] ->
> m0 (String, String)' In the return type of a call of `foldM'
>
> thanks,
> m.
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>

From anguscomber at gmail.com  Tue Dec 31 14:46:03 2013
From: anguscomber at gmail.com (Angus Comber)
Date: Tue, 31 Dec 2013 14:46:03 +0000
Subject: [Haskell-beginners] Trying to understand function types eg iterate
	(a -> a)
Message-ID: <CAAtGUhV_mWHknBSRQ=N_8LUrB1=8oVr39AKxk+E1PfsRcr9+tQ@mail.gmail.com>

iterate' :: (a -> a) -> a -> [a]

I am trying going to go ahead and write my own iterate function.  But
before I do I want to be clear on types.

Looking at  :: (a -> a) -> a -> [a]

The first part is (a -> a)  Now because it is in parentheses it is a
function?

I can call iterate like this:
take 5 $ iterate (*2) 5

So (*2) is a possible function.  Does the brackets mean it is a function,
the left hand a is indicating a general type and the right hand a means the
return type must be the same as the function type.  Eg in the case of (*2)
the 2 is an Int so the function returns and Int?  Is my understanding
correct?

How could this be better explained?

The last bit is easier to understand.  a -> [a] meaning a singleton of
general type and [a] means a list of same type.
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From peter.hall at memorphic.com  Tue Dec 31 14:53:44 2013
From: peter.hall at memorphic.com (Peter Hall)
Date: Tue, 31 Dec 2013 14:53:44 +0000
Subject: [Haskell-beginners] Trying to understand function types eg
 iterate (a -> a)
In-Reply-To: <CAAtGUhV_mWHknBSRQ=N_8LUrB1=8oVr39AKxk+E1PfsRcr9+tQ@mail.gmail.com>
References: <CAAtGUhV_mWHknBSRQ=N_8LUrB1=8oVr39AKxk+E1PfsRcr9+tQ@mail.gmail.com>
Message-ID: <CAA6hAk5kvgH5kiVZeidbOp0QJso5ipLQ0arA2eFXFEsePVYVMQ@mail.gmail.com>

When you wrap an operator in parentheses and supply just one of its
arguments, then it's called an operator section. It's syntactic sugar for
partially applying the operator, as you can with other functions.

This:
    (*2)

is exactly equivalent to:
    (\x -> x*2)

and it's type is something like:
    Int -> Int

And:
    (2:)

is equivalent to:
    (\x -> 2:x)

etc



On 31 December 2013 14:46, Angus Comber <anguscomber at gmail.com> wrote:

> iterate' :: (a -> a) -> a -> [a]
>
> I am trying going to go ahead and write my own iterate function.  But
> before I do I want to be clear on types.
>
> Looking at  :: (a -> a) -> a -> [a]
>
> The first part is (a -> a)  Now because it is in parentheses it is a
> function?
>
> I can call iterate like this:
> take 5 $ iterate (*2) 5
>
> So (*2) is a possible function.  Does the brackets mean it is a function,
> the left hand a is indicating a general type and the right hand a means the
> return type must be the same as the function type.  Eg in the case of (*2)
> the 2 is an Int so the function returns and Int?  Is my understanding
> correct?
>
> How could this be better explained?
>
> The last bit is easier to understand.  a -> [a] meaning a singleton of
> general type and [a] means a list of same type.
>
>
>
>
>
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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From idivyanshu.ranjan at gmail.com  Tue Dec 31 14:55:13 2013
From: idivyanshu.ranjan at gmail.com (divyanshu ranjan)
Date: Tue, 31 Dec 2013 20:25:13 +0530
Subject: [Haskell-beginners] Trying to understand function types eg
 iterate (a -> a)
In-Reply-To: <CAAtGUhV_mWHknBSRQ=N_8LUrB1=8oVr39AKxk+E1PfsRcr9+tQ@mail.gmail.com>
References: <CAAtGUhV_mWHknBSRQ=N_8LUrB1=8oVr39AKxk+E1PfsRcr9+tQ@mail.gmail.com>
Message-ID: <CAL9hw26ahZ7gPDm0qeBdVg-+-hR9QUc2DaLNvQBcxjnd1Pvm9g@mail.gmail.com>

Hi Angus,

   Your understanding is correct. Parenthesis is need in a -> a to specify
that it is function from a to a because associativity of -> is from right
to left. (*2) is section, you can read more
   about here :
http://www.haskell.org/haskellwiki/Section_of_an_infix_operator.

   Type of (*2) is (Num a) :: a -> a rather than particular type Int.


Thanks
Divyanshu Ranjan





On Tue, Dec 31, 2013 at 8:16 PM, Angus Comber <anguscomber at gmail.com> wrote:

> iterate' :: (a -> a) -> a -> [a]
>
> I am trying going to go ahead and write my own iterate function.  But
> before I do I want to be clear on types.
>
> Looking at  :: (a -> a) -> a -> [a]
>
> The first part is (a -> a)  Now because it is in parentheses it is a
> function?
>
> I can call iterate like this:
> take 5 $ iterate (*2) 5
>
> So (*2) is a possible function.  Does the brackets mean it is a function,
> the left hand a is indicating a general type and the right hand a means the
> return type must be the same as the function type.  Eg in the case of (*2)
> the 2 is an Int so the function returns and Int?  Is my understanding
> correct?
>
> How could this be better explained?
>
> The last bit is easier to understand.  a -> [a] meaning a singleton of
> general type and [a] means a list of same type.
>
>
>
>
>
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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From anguscomber at gmail.com  Tue Dec 31 18:48:59 2013
From: anguscomber at gmail.com (Angus Comber)
Date: Tue, 31 Dec 2013 18:48:59 +0000
Subject: [Haskell-beginners] How to get each list in a list of lists for
	filter
Message-ID: <CAAtGUhXO=spFyLeZh3V3JQ=h+tqKrH3k2NcdEW-MNf91Xha57w@mail.gmail.com>

I am getting a list of lists from chop9.  I want to somehow filter each
element in the list.  How do I do that.

I have encoded binary data eg [1,1,0,0,1,0] etc

Each 9th bit is a parity bit which is checked using this function:

type Bit = Int

paritychecker :: [Bit] -> Bool
paritychecker xs | length xs == 9 && ((sum (init xs)) `mod` 2) == (last xs)
= True
                 | otherwise = False


In the stream (the list) I use chop to retrieve each block of 9 bits as in:

chop9 :: [Bit] -> [[Bit]]
chop9 [] = []
chop9 bits = take 8 bits : chop9 (drop 8 bits)

I have been playing with this sort of thing:
filter paritychecker ??? chop9 [1,0,0,0,1,1,1,0,0,...]

But doesn't work.

I want to end up with all the 9 bit chunks which pass the filter.  So my
end type should be [[Bit]]

paritychecker requires a list - eg [Bit] . So I want to run paritychecker
on each element returned from chop9.  How do I do that?

Example encoded data stream:
[1,0,0,0,1,1,1,0,0,1,1,1,0,1,1,1,0,0,1,0,1,0,0,1,1,0,0,0,1,0,0,1,1,1,0,0,0,0,1,0,1,1,1,0,0,1,0,0,1,1,1,1,0,1]

Angus
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From idivyanshu.ranjan at gmail.com  Tue Dec 31 18:57:07 2013
From: idivyanshu.ranjan at gmail.com (divyanshu ranjan)
Date: Wed, 1 Jan 2014 00:27:07 +0530
Subject: [Haskell-beginners] How to get each list in a list of lists for
	filter
In-Reply-To: <CAAtGUhXO=spFyLeZh3V3JQ=h+tqKrH3k2NcdEW-MNf91Xha57w@mail.gmail.com>
References: <CAAtGUhXO=spFyLeZh3V3JQ=h+tqKrH3k2NcdEW-MNf91Xha57w@mail.gmail.com>
Message-ID: <CAL9hw25LhKbZnx2mRu29QBPNk-OjGdpFNKUa0pCBD9_=7GSDGw@mail.gmail.com>

Hi Angus,
    Try placing $ in place of ???.  Type of filter is (a->Bool) -> [a] ->
[a]. $ is of type (a->b) -> a -> b  but it's low priority so left and right
hand side is calculated before function application.

Thanks
Divyanshu Ranjan


On Wed, Jan 1, 2014 at 12:18 AM, Angus Comber <anguscomber at gmail.com> wrote:

> I am getting a list of lists from chop9.  I want to somehow filter each
> element in the list.  How do I do that.
>
> I have encoded binary data eg [1,1,0,0,1,0] etc
>
> Each 9th bit is a parity bit which is checked using this function:
>
> type Bit = Int
>
> paritychecker :: [Bit] -> Bool
> paritychecker xs | length xs == 9 && ((sum (init xs)) `mod` 2) == (last
> xs) = True
>                  | otherwise = False
>
>
> In the stream (the list) I use chop to retrieve each block of 9 bits as in:
>
> chop9 :: [Bit] -> [[Bit]]
> chop9 [] = []
> chop9 bits = take 8 bits : chop9 (drop 8 bits)
>
> I have been playing with this sort of thing:
> filter paritychecker ??? chop9 [1,0,0,0,1,1,1,0,0,...]
>
>  But doesn't work.
>
> I want to end up with all the 9 bit chunks which pass the filter.  So my
> end type should be [[Bit]]
>
> paritychecker requires a list - eg [Bit] . So I want to run paritychecker
> on each element returned from chop9.  How do I do that?
>
> Example encoded data stream:
>
> [1,0,0,0,1,1,1,0,0,1,1,1,0,1,1,1,0,0,1,0,1,0,0,1,1,0,0,0,1,0,0,1,1,1,0,0,0,0,1,0,1,1,1,0,0,1,0,0,1,1,1,1,0,1]
>
> Angus
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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From bo at ct.de  Tue Dec 31 20:34:44 2013
From: bo at ct.de (=?ISO-8859-1?Q?Harald_B=F6geholz?=)
Date: Tue, 31 Dec 2013 21:34:44 +0100
Subject: [Haskell-beginners] How to get each list in a list of lists for
 filter
In-Reply-To: <CAAtGUhXO=spFyLeZh3V3JQ=h+tqKrH3k2NcdEW-MNf91Xha57w@mail.gmail.com>
References: <CAAtGUhV_mWHknBSRQ=N_8LUrB1=8oVr39AKxk+E1PfsRcr9+tQ@mail.gmail.com>
 <CAAtGUhWfmF7JQvSh270xN9KbHVa2fxCe6f=WxYxTchqu79fPkg@mail.gmail.com>
 <CAAtGUhUA3Mf0GeX0mcMamtDPdp7OVS3pwKBPjyk2inS4QcJ8zA@mail.gmail.com>
 <CAAtGUhWbe-os+bEM3xNAc2PGO52xXE7g2PDjq0rXOOTKr+Kn0Q@mail.gmail.com>
 <CAAtGUhX80Ro0Dvc8PrVWhLDcKjCWqyZPNAAW1vor6kf=y=jcpA@mail.gmail.com>
 <CAAtGUhXO=spFyLeZh3V3JQ=h+tqKrH3k2NcdEW-MNf91Xha57w@mail.gmail.com>
Message-ID: <52C32A64.5000005@ct.de>

Am 31.12.13 19:48, schrieb Angus Comber:
> I am getting a list of lists from chop9.  I want to somehow filter each
> element in the list.  How do I do that.
> 
> I have encoded binary data eg [1,1,0,0,1,0] etc
> 
> Each 9th bit is a parity bit which is checked using this function:
> 
> type Bit = Int
> 
> paritychecker :: [Bit] -> Bool
> paritychecker xs | length xs == 9 && ((sum (init xs)) `mod` 2) == (last xs)
> = True
>                  | otherwise = False
> 
> 
> In the stream (the list) I use chop to retrieve each block of 9 bits as in:
> 
> chop9 :: [Bit] -> [[Bit]]
> chop9 [] = []
> chop9 bits = take 8 bits : chop9 (drop 8 bits)
> 
> I have been playing with this sort of thing:
> filter paritychecker ??? chop9 [1,0,0,0,1,1,1,0,0,...]
> 
> But doesn't work.

Could a simple typo be the problem?

Shouldn't chop9 .. take 9 bits ... and ... drop 9 bits ... instead of 8?

Harald
-- 
Harald B?geholz    <bo at ct.de> (PGP key available from servers)
Redaktion c't      Tel.: +49 511 5352-300  Fax: +49 511 5352-417
                   http://www.ct.de/

                   int f[9814],b,c=9814,g,i;long a=1e4,d,e,h;
                   main(){for(;b=c,c-=14;i=printf("%04d",e+d/a),e=d%a)
                   while(g=--b*2)d=h*b+a*(i?f[b]:a/5),h=d/--g,f[b]=d%g;}
                                                          (Arndt/Haenel)

                   Affe Apfel Vergaser

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