From laiboonh at gmail.com  Tue Nov  1 15:42:06 2016
From: laiboonh at gmail.com (Lai Boon Hui)
Date: Tue, 1 Nov 2016 23:42:06 +0800
Subject: [Haskell-beginners] Sum a tuple of Monoids
Message-ID: <CAJdQggmVvzhP+wNSN6RaZRs5NQS2pnhbh5RkXQdQOK=AE8dp8w@mail.gmail.com>

Hi all,

Is it possible to sum a tuple of monoids for example

sum (Just 1, Nothing)

expected result Just 1

sum (Just 1, Just 2)

expected result Just 3

-- 
Best Regards,
Boon Hui
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From imantc at gmail.com  Tue Nov  1 15:55:38 2016
From: imantc at gmail.com (Imants Cekusins)
Date: Tue, 1 Nov 2016 16:55:38 +0100
Subject: [Haskell-beginners] Sum a tuple of Monoids
In-Reply-To: <CAJdQggmVvzhP+wNSN6RaZRs5NQS2pnhbh5RkXQdQOK=AE8dp8w@mail.gmail.com>
References: <CAJdQggmVvzhP+wNSN6RaZRs5NQS2pnhbh5RkXQdQOK=AE8dp8w@mail.gmail.com>
Message-ID: <CAP1qinYNVj=01BTSayKZxKAqQr=1_crBvU0vRLdtaTzn1J_+kA@mail.gmail.com>

> sum a tuple of monoids

here is something, not quite what you are looking for, but close:

Monoid
<http://hackage.haskell.org/package/base-4.9.0.0/docs/Data-Monoid.html#t:Monoid>
a
=> Monoid
<http://hackage.haskell.org/package/base-4.9.0.0/docs/Data-Monoid.html#t:Monoid>
 (Maybe
<http://hackage.haskell.org/package/base-4.9.0.0/docs/Data-Maybe.html#t:Maybe>
 a)
(Monoid
<http://hackage.haskell.org/package/base-4.9.0.0/docs/Data-Monoid.html#t:Monoid>
 a, Monoid
<http://hackage.haskell.org/package/base-4.9.0.0/docs/Data-Monoid.html#t:Monoid>
b)
=> Monoid
<http://hackage.haskell.org/package/base-4.9.0.0/docs/Data-Monoid.html#t:Monoid>
(a,
b)

mappend (Just [1], Just [2,3]) (Nothing, Just [5])::(Maybe [Int],Maybe
[Int])
(Just [1],Just [2,3,5])

​
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From toad3k at gmail.com  Tue Nov  1 15:58:07 2016
From: toad3k at gmail.com (David McBride)
Date: Tue, 1 Nov 2016 11:58:07 -0400
Subject: [Haskell-beginners] Sum a tuple of Monoids
In-Reply-To: <CAJdQggmVvzhP+wNSN6RaZRs5NQS2pnhbh5RkXQdQOK=AE8dp8w@mail.gmail.com>
References: <CAJdQggmVvzhP+wNSN6RaZRs5NQS2pnhbh5RkXQdQOK=AE8dp8w@mail.gmail.com>
Message-ID: <CAN+Tr41QHe377c2z+92fjy7GmYpFt-VC47JFRf=7Vtsizk2zAg@mail.gmail.com>

I don't know if there is generally, but some people would use the lens
library to do such things.

import Control.Lens
> sumOf (each . _Just) (Just 1, Nothing, Just 2)
3

Just keep in mind that each member of the tuple must be the same type.

On Tue, Nov 1, 2016 at 11:42 AM, Lai Boon Hui <laiboonh at gmail.com> wrote:

> Hi all,
>
> Is it possible to sum a tuple of monoids for example
>
> sum (Just 1, Nothing)
>
> expected result Just 1
>
> sum (Just 1, Just 2)
>
> expected result Just 3
>
> --
> Best Regards,
> Boon Hui
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
>
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From jolivetdesonte at yahoo.com  Thu Nov  3 04:49:36 2016
From: jolivetdesonte at yahoo.com (Desonte Jolivet)
Date: Thu, 3 Nov 2016 04:49:36 +0000 (UTC)
Subject: [Haskell-beginners] =?utf-8?q?Java-Bridge=2C_Ambiguous_occurrence?=
	=?utf-8?b?IOKAmDwk4oCZ?=
References: <1487192299.175038.1478148576572.ref@mail.yahoo.com>
Message-ID: <1487192299.175038.1478148576572@mail.yahoo.com>

Hello All:
Im interested interfacing with the JVM through Haskell and I found this neat library on Hackag name java-bridge although when I try and install with cabal I get the below error, "Ambiguous occurrence ‘<$’". Any tips on how to clear this up or how I should proceed would be very helpful, Thank you all in advance.
src/Foreign/Java/IO.hs:5:7: Warning:    -XOverlappingInstances is deprecated: instead use per-instance pragmas OVERLAPPING/OVERLAPPABLE/OVERLAPS[ 1 of 24] Compiling Foreign.Java.Tutorial ( src/Foreign/Java/Tutorial.hs, dist/build/Foreign/Java/Tutorial.o )[ 2 of 24] Compiling Foreign.Java.IO  ( src/Foreign/Java/IO.hs, dist/build/Foreign/Java/IO.o )[ 3 of 24] Compiling Foreign.Java.Control ( src/Foreign/Java/Control.hs, dist/build/Foreign/Java/Control.o )[ 4 of 24] Compiling Foreign.Java.Bindings.ReflectHaskell ( src/Foreign/Java/Bindings/ReflectHaskell.hs, dist/build/Foreign/Java/Bindings/ReflectHaskell.o )[ 5 of 24] Compiling Foreign.Java.Bindings.Haskell2Java ( dist/build/Foreign/Java/Bindings/Haskell2Java.hs, dist/build/Foreign/Java/Bindings/Haskell2Java.o )[ 6 of 24] Compiling Foreign.Java.Bindings.HaskellTypes ( src/Foreign/Java/Bindings/HaskellTypes.hs, dist/build/Foreign/Java/Bindings/HaskellTypes.o )[ 7 of 24] Compiling Foreign.Java.Bindings.JavaSE6 ( src/Foreign/Java/Bindings/JavaSE6.hs, dist/build/Foreign/Java/Bindings/JavaSE6.o )[ 8 of 24] Compiling Foreign.Java.Utils ( src/Foreign/Java/Utils.hs, dist/build/Foreign/Java/Utils.o )[ 9 of 24] Compiling Foreign.Java.Bindings.JavaTypes ( src/Foreign/Java/Bindings/JavaTypes.hs, dist/build/Foreign/Java/Bindings/JavaTypes.o )[10 of 24] Compiling Foreign.Java.Util ( src/Foreign/Java/Util.hs, dist/build/Foreign/Java/Util.o )
src/Foreign/Java/Util.hs:5:19:    Ambiguous occurrence ‘<$’    It could refer to either ‘Foreign.Java.Util.<$’,                             defined at src/Foreign/Java/Util.hs:24:1                          or ‘Prelude.<$’,                             imported from ‘Prelude’ at src/Foreign/Java/Util.hs:4:8-24                             (and originally defined in ‘GHC.Base’)cabal: Error: some packages failed to install:java-bridge-0.20130606.3 failed during the building phase. The exception was:ExitFailure 1

-Jo
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From defigueiredo at ucdavis.edu  Thu Nov  3 15:43:33 2016
From: defigueiredo at ucdavis.edu (Dimitri DeFigueiredo)
Date: Thu, 3 Nov 2016 09:43:33 -0600
Subject: [Haskell-beginners] Constructor classes and type classes.
In-Reply-To: <mailman.7.1477915202.5192.beginners@haskell.org>
References: <mailman.7.1477915202.5192.beginners@haskell.org>
Message-ID: <80e94e0d-d05b-3606-290f-edcd7d8ef25b@ucdavis.edu>

Hi Patrick,

I am not sure I understand what you are trying to do, but here are some
thoughts.

- your use of the names `typeVar` and `typeCons` make total sense to me.
But your name `dataCons` in the definition of SetClass2 does not. You
are only talking about types here. All you are doing is talking about
*type* constructors. You are not constructing a specific value of that
type. Maybe one way to see the difference between the type constructors
and the data constructors is to change your first line to:

data SetType typeVar = SetTypeDataConstructor [typeVar] deriving Show

- I also don't understand why you named your type variable
`dataVariable` instead of sticking to `typeVar` in SetClass3. It is a
*type* variable in the type signature of the functions in the type class.

- I don't understand what you mean by a "constructor class". My simple
understanding of what a type constructors and data constructors are is here
https://wiki.haskell.org/Constructor#Type_constructor.

- I don't see the terms super class and sub class ever used in haskell
land. Although I do understand they make sense, I think they are really
OO terms. I've tried to map OO concepts into haskell and there are many
different ways to do it. The best description of all those ways that I
found was in Oleg Kiselyov's work
https://arxiv.org/pdf/cs/0509027.pdf

- I think parametric polymorphism as used in haskell forces us to
compare types in terms of equality constraints (this type is "the same"
as that), whereas subtype polymorphism as used in OO languages forces us
to think in terms of inequalities (this type is "more specific" than
that). I think those force fundamentally different ways to think about
and model your problems. I would encourage you to use equality as much
as possible, but if you want to model subtyping in haskell, I think
Oleg's work above has a few approaches that I think are better than type
classes. In particular, in OO there was always an ambiguity between
modelling subtyping with inheritance or with a "has a" relationship when
the subclass explicitly contains an object of the superclass. You can
use the latter idea in haskell, Oleg's work has a good way to do it.

Hope this helps.

Cheers,

Dimitri


> From: PATRICK BROWNE <patrick.browne at dit.ie>
> To: The Haskell-Beginners Mailing List - Discussion of primarily
> 	beginner-level topics related to Haskell <beginners at haskell.org>
> Subject: [Haskell-beginners] Constructor classes and type classes.
> Message-ID:
> 	<CAGFLrKfQVaQQJybMTn-pJksV1VKUXrmBks14Jkm==Zqt=bdy5A at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> {-
> I am trying to understand constructor classes and their relationship with
> ordinary type classes.
> I wrote the code below to help me understand the distinction. The code is
> only for explanatory purposes, set operations use a tuple syntax.
>
> I use the naming convention of 'typeVar', 'typeCons', and 'dataCons' for
> type variables, type constructors, and data constructors respectively.
> Question1:
> Is my naming convention correct?
> I am particularly concerned about SetClass3 where the super class seems to
> use a type constructor but the subclass seems to use the same term as a
> data constructor.
>
> Q2:
> In this case constructor classes and type classes seem to provide similar
> functionality.
> In general what situation are each best suited?
> -}
>
> import Data.List
> data SetType typeVar = SetType [typeVar] deriving Show
>
>
> class SetClass1 typeCons where
>   member1 ::   Eq typeVar  =>  (typeVar, typeCons typeVar)  -> Bool
>   intersect1 ::  (Eq typeVar,Show typeVar) =>  (typeCons typeVar, typeCons
> typeVar) -> typeCons typeVar
>
>
> class  SetClass2 dataCons typeVar where
>   member2 ::  (typeVar, (dataCons typeVar))  -> Bool
>   intersect2 :: (dataCons typeVar, dataCons typeVar) -> dataCons typeVar
>
>
> class SetClass1 typeCons => SetClass3  typeCons dataVariable where
>  union3 ::  (Eq dataVariable,Show dataVariable) =>  (typeCons dataVariable,
> typeCons dataVariable) -> typeCons dataVariable
>
> instance SetClass1 SetType where
>  member1 (x ,(SetType y)) = elem  x y
>  intersect1 ((SetType x),(SetType y)) = SetType (intersect x y)
>
> instance SetClass2 SetType Int where
>  member2 (x ,SetType y) =   elem  x y
>  intersect2 (SetType x,SetType y) = SetType (intersect x y)
>
> instance SetClass3 SetType Int where
>  union3 (SetType x,SetType y) = SetType (union x y)
>
>
> test1a = member1 (1, (SetType [1,2]))
> test1b = intersect1 ((SetType [1,3,4]),(SetType [1,2]))
> test2a = member2 (1, (SetType [1::Int]))
> test2b = intersect2 ((SetType [1::Int]), (SetType [(1::Int)]))
> test3a = union3 ((SetType [1::Int,2::Int,3::Int]),(SetType [4::Int,5::Int]))
>

-- 
2E45 D376 A744 C671 5100 A261 210B 8461 0FB0 CA1F


-- 
2E45 D376 A744 C671 5100 A261 210B 8461 0FB0 CA1F

From patrick.browne at dit.ie  Thu Nov  3 17:51:14 2016
From: patrick.browne at dit.ie (PATRICK BROWNE)
Date: Thu, 3 Nov 2016 17:51:14 +0000
Subject: [Haskell-beginners] Constructor classes and type classes.
In-Reply-To: <80e94e0d-d05b-3606-290f-edcd7d8ef25b@ucdavis.edu>
References: <mailman.7.1477915202.5192.beginners@haskell.org>
 <80e94e0d-d05b-3606-290f-edcd7d8ef25b@ucdavis.edu>
Message-ID: <CAGFLrKcdPCPZBoXy2RxmXLMmNme5w+YHoE2CxpD3QEntEY4b1w@mail.gmail.com>

Dimitri,
Thanks for taking the time and effort to respond. Your comments have
clarified some of my confusion. My motivation is that I am trying to
implement the code from a paper
<http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.36.9395> with the
following data and classes:

{-# LANGUAGE MultiParamTypeClasses #-}
data TimeFacts t = Bef (t, t, TimeFacts t) | New

class SetClass t  where
class SetClass t => Time l t  where
class Time l t => TimeE l t where
class Time l t => TimeTO l t where

However I cannot get the instances to compile:
instance SetClass (TimeFacts t) where -- OK
instance (SetClass t) => Time TimeFacts t where -- Expecting one more
argument to 'TimeFacts'
instance TimeE TimeFacts t where -- Expecting one more argument to
'TimeFacts'
instance TimeTO TimeFacts t where -- Expecting one more argument to
'TimeFacts'


Note, I am only using the headings for the classes and instances, which
should be OK.
Any pointers to a solution would be much appreciated.

Regards,
Pat

-- 


This email originated from DIT. If you received this email in error, please 
delete it from your system. Please note that if you are not the named 
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From imantc at gmail.com  Thu Nov  3 18:05:10 2016
From: imantc at gmail.com (Imants Cekusins)
Date: Thu, 3 Nov 2016 19:05:10 +0100
Subject: [Haskell-beginners] Constructor classes and type classes.
In-Reply-To: <CAGFLrKcdPCPZBoXy2RxmXLMmNme5w+YHoE2CxpD3QEntEY4b1w@mail.gmail.com>
References: <mailman.7.1477915202.5192.beginners@haskell.org>
 <80e94e0d-d05b-3606-290f-edcd7d8ef25b@ucdavis.edu>
 <CAGFLrKcdPCPZBoXy2RxmXLMmNme5w+YHoE2CxpD3QEntEY4b1w@mail.gmail.com>
Message-ID: <CAP1qinaGvO+X5VZMR4gJu8emJDT8PEC5-r0APSr5S1g1YsN_8Q@mail.gmail.com>

this builds. not sure if the instances are as intended


{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances #-}
module SetClass where

data TimeFacts t = Bef (t, t, TimeFacts t) | New

class SetClass t  where
class SetClass t => Time l t  where
class Time l t => TimeE l t where
class Time l t => TimeTO l t where


instance SetClass (TimeFacts t) where -- OK
instance (SetClass t) => Time (TimeFacts t) t where
instance (SetClass t) => TimeE (TimeFacts t) t where
instance (SetClass t) => TimeTO (TimeFacts t) t where

​
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From toad3k at gmail.com  Thu Nov  3 19:58:01 2016
From: toad3k at gmail.com (David McBride)
Date: Thu, 3 Nov 2016 15:58:01 -0400
Subject: [Haskell-beginners]
	=?utf-8?q?Java-Bridge=2C_Ambiguous_occurrence?=
	=?utf-8?b?IOKAmDwk4oCZ?=
In-Reply-To: <1487192299.175038.1478148576572@mail.yahoo.com>
References: <1487192299.175038.1478148576572.ref@mail.yahoo.com>
 <1487192299.175038.1478148576572@mail.yahoo.com>
Message-ID: <CAN+Tr42VjsMr56WyGzDmJ7msv+ocSMchGbawOu_bxg1gQ52hgQ@mail.gmail.com>

That specific error can be fixed by simply removing that function and its
export from src/Foreign/Java/Util.hs as it is exported by Prelude now and
there is no reason for it to be in his code.

Given the amount of bitrot that package has probably suffered, I'm not sure
how much faith I have that it will work.  That said, if you are
enterprising it probably wouldn't be too hard to fix all these errors.

In other news there are some other recent developments on this front.
There is an inline-java project that looks very promising and may actually
be very simple to get up and working with stack.

https://github.com/tweag/inline-java#readme

On Thu, Nov 3, 2016 at 12:49 AM, Desonte Jolivet <jolivetdesonte at yahoo.com>
wrote:

> Hello All:
>
> Im interested interfacing with the JVM through Haskell and I found this
> neat library on Hackag name java-bridge although when I try and install
> with cabal I get the below error, "Ambiguous occurrence ‘<$’". Any tips on
> how to clear this up or how I should proceed would be very helpful, Thank
> you all in advance.
>
> src/Foreign/Java/IO.hs:5:7: Warning:
>     -XOverlappingInstances is deprecated: instead use per-instance pragmas
> OVERLAPPING/OVERLAPPABLE/OVERLAPS
> [ 1 of 24] Compiling Foreign.Java.Tutorial ( src/Foreign/Java/Tutorial.hs,
> dist/build/Foreign/Java/Tutorial.o )
> [ 2 of 24] Compiling Foreign.Java.IO  ( src/Foreign/Java/IO.hs,
> dist/build/Foreign/Java/IO.o )
> [ 3 of 24] Compiling Foreign.Java.Control ( src/Foreign/Java/Control.hs,
> dist/build/Foreign/Java/Control.o )
> [ 4 of 24] Compiling Foreign.Java.Bindings.ReflectHaskell (
> src/Foreign/Java/Bindings/ReflectHaskell.hs, dist/build/Foreign/Java/Bindings/ReflectHaskell.o
> )
> [ 5 of 24] Compiling Foreign.Java.Bindings.Haskell2Java (
> dist/build/Foreign/Java/Bindings/Haskell2Java.hs, dist/build/Foreign/Java/Bindings/Haskell2Java.o
> )
> [ 6 of 24] Compiling Foreign.Java.Bindings.HaskellTypes (
> src/Foreign/Java/Bindings/HaskellTypes.hs, dist/build/Foreign/Java/Bindings/HaskellTypes.o
> )
> [ 7 of 24] Compiling Foreign.Java.Bindings.JavaSE6 (
> src/Foreign/Java/Bindings/JavaSE6.hs, dist/build/Foreign/Java/Bindings/JavaSE6.o
> )
> [ 8 of 24] Compiling Foreign.Java.Utils ( src/Foreign/Java/Utils.hs,
> dist/build/Foreign/Java/Utils.o )
> [ 9 of 24] Compiling Foreign.Java.Bindings.JavaTypes (
> src/Foreign/Java/Bindings/JavaTypes.hs, dist/build/Foreign/Java/Bindings/JavaTypes.o
> )
> [10 of 24] Compiling Foreign.Java.Util ( src/Foreign/Java/Util.hs,
> dist/build/Foreign/Java/Util.o )
>
> src/Foreign/Java/Util.hs:5:19:
>     Ambiguous occurrence ‘<$’
>     It could refer to either ‘Foreign.Java.Util.<$’,
>                              defined at src/Foreign/Java/Util.hs:24:1
>                           or ‘Prelude.<$’,
>                              imported from ‘Prelude’ at
> src/Foreign/Java/Util.hs:4:8-24
>                              (and originally defined in ‘GHC.Base’)
> cabal: Error: some packages failed to install:
> java-bridge-0.20130606.3 failed during the building phase. The exception
> was:
> ExitFailure 1
>
>
> -Jo
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
>
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From patrick.browne at dit.ie  Fri Nov  4 00:10:26 2016
From: patrick.browne at dit.ie (PATRICK BROWNE)
Date: Fri, 4 Nov 2016 00:10:26 +0000
Subject: [Haskell-beginners] Constructor classes and type classes.
Message-ID: <CAGFLrKcRtO6zBYPtwLNTBbfcfxTRS92vKWf0TC=mXrkmtX9euA@mail.gmail.com>

Imants
Thanks for the sanity check on the instances.

I am concerned about the use of the function immsucc' from the same paper
<http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.36.9395>, which is
defined in instances the Time class (but omitted from the class). The
function  immsucc' is first used without arguments, which to me implies
that it 'might' a function passed to the higher-order closure function. It
is then used as just an ordinary function with arguments. I have found a
version of closure based on Craft of Function Programming.
<https://github.com/buntine/Haskell--Craft-of-FP/blob/master/AbsTypes/Relation.lhs>
which
does not require a function as an argument.

So basically my question is: does the usage of immsucc' make sense in the
code below?, do the types match up?
Regards,
Pat



data TimeFacts t = Bef (t, t, TimeFacts t) | New

class SetClass t => Time l t where
 new :: (t, t) -> l t
 bef :: (t, t, l t) -> l t
 succ , pred :: (t, l t) -> Set t
 immsucc , immpred :: (t, l t) -> Set t
 before, after :: (t, t, l t) -> Bool
 immedbefore, immedafter :: (t, t, l t) -> Bool
 immedafter (a, b, t) = immedbefore (b, a, t)
 after (a, b, t) = before (b, a, t)
 before (a, b, t) = memberInSet (b, succ (a, t))
 succ (a, tl) = closure ([a], immsucc' , tl)
 pred (a, tl) = closure ([a], immpred' , tl)
 immsucc (a, tl) = immsucc' ([a], [], tl)
 immpred (a, tl) = immpred' ([a], [], tl)

instance (SetClass t) => Time TimeFacts t where
 immsucc’ (a, s, New ) = s
 immsucc’ (a, s, Bef (e, f, tt)) = if memberInSet (e,a) then immsucc’ (a,
insertInSet (f,s), tt) else immsucc’ (a, s,tt)


On 3 November 2016 at 18:05, Imants Cekusins <imantc at gmail.com> wrote:

> this builds. not sure if the instances are as intended
>
>
> {-# LANGUAGE MultiParamTypeClasses, FlexibleInstances #-}
> module SetClass where
>
> data TimeFacts t = Bef (t, t, TimeFacts t) | New
>
> class SetClass t  where
> class SetClass t => Time l t  where
> class Time l t => TimeE l t where
> class Time l t => TimeTO l t where
>
>
> instance SetClass (TimeFacts t) where -- OK
> instance (SetClass t) => Time (TimeFacts t) t where
> instance (SetClass t) => TimeE (TimeFacts t) t where
> instance (SetClass t) => TimeTO (TimeFacts t) t where
>
> ​
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
>

-- 


This email originated from DIT. If you received this email in error, please 
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the contents of this email or attachments is prohibited. www.dit.ie

Is ó ITBÁC a tháinig an ríomhphost seo. Má fuair tú an ríomhphost seo trí 
earráid, scrios de do chóras é le do thoil. Tabhair ar aird, mura tú an 
seolaí ainmnithe, go bhfuil dianchosc ar aon nochtadh, aon chóipeáil, aon 
dáileadh nó ar aon ghníomh a dhéanfar bunaithe ar an ábhar atá sa 
ríomhphost nó sna hiatáin seo. www.dit.ie

Tá ITBÁC ag aistriú go Gráinseach Ghormáin – DIT is on the move to 
Grangegorman <http://www.dit.ie/grangegorman>
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From brutallesale at gmail.com  Thu Nov 10 18:44:17 2016
From: brutallesale at gmail.com (sasa bogicevic)
Date: Thu, 10 Nov 2016 19:44:17 +0100
Subject: [Haskell-beginners] OI UTCTime to String
Message-ID: <7085A8E2-7469-440C-BD04-747A056008B5@gmail.com>

Hi All,

This is a small program

{-# LANGUAGE OverloadedStrings #-}
module Main where

import           Control.Monad.IO.Class     (liftIO)
import qualified Data.ByteString.Lazy.Char8 as L
import           Data.Time
import           Network                    (withSocketsDo)
import           Network.HTTP.Conduit


createRequestData today = [("index:brKursneListe",""),
 ("index:year","2016"),
 ("index:inputCalendar1", today),
 ("index:vrsta","3"),
 ("index:prikaz","0"),
 ("index:buttonShow","Prikazi")]


timeFromString  s = parseTimeOrError True defaultTimeLocale "%d %b %Y %l:%M %p" s

formatDateString time = formatTime defaultTimeLocale "%m/%d/%Y" time

getDateString = getCurrentTime

getFormatedDate  = formatDateString $ timeFromString getDateString

main = do
	print $ getFormatedDate


And here is my error

main.hs:25:54: error:
   • Couldn't match type ‘IO UTCTime’ with ‘[Char]’
     Expected type: String
       Actual type: IO UTCTime
   • In the first argument of ‘timeFromString’, namely ‘getDateString’
     In the second argument of ‘($)’, namely
       ‘timeFromString getDateString’
     In the expression: formatDateString $ timeFromString getDateString

Thanks!


From fa-ml at ariis.it  Thu Nov 10 18:52:21 2016
From: fa-ml at ariis.it (Francesco Ariis)
Date: Thu, 10 Nov 2016 19:52:21 +0100
Subject: [Haskell-beginners] OI UTCTime to String
In-Reply-To: <7085A8E2-7469-440C-BD04-747A056008B5@gmail.com>
References: <7085A8E2-7469-440C-BD04-747A056008B5@gmail.com>
Message-ID: <20161110185221.GA18500@casa.casa>

On Thu, Nov 10, 2016 at 07:44:17PM +0100, sasa bogicevic wrote:
> Hi All,
> 
> This is a small program
>
> [...]

Hey Sasa,
If we put this into ghci

    λ> :t formatDateString $ timeFromString _

the "hole" tells us we need something of type String, but `getDateString`
is not!

    λ> :t getDateString
    getDateString :: IO UTCTime

That means you have to bind it inside a `do` block (or use >>=).
Ask for more if I was not clear!

From nrujac at gmail.com  Thu Nov 10 19:07:09 2016
From: nrujac at gmail.com (Arjun Comar)
Date: Thu, 10 Nov 2016 19:07:09 +0000
Subject: [Haskell-beginners] OI UTCTime to String
In-Reply-To: <20161110185221.GA18500@casa.casa>
References: <7085A8E2-7469-440C-BD04-747A056008B5@gmail.com>
 <20161110185221.GA18500@casa.casa>
Message-ID: <CADjRcrUyNrgc7-yeta4myO-X-1x53gmrtq8PX23dsJbq=TNLyg@mail.gmail.com>

Adding to Francesco's reply, UTCTime is not a String either. Luckily, it
does have a Show instance however, which means you probably want something
like:

    getDateString = do
        date <- getCurrentTime
        return $ show date

Or, more simply: getDateString = fmap show getCurrentTime

You will still need to use bind, fmap, or do to get at the actual date
string however.

Thanks,
Arjun

On Thu, Nov 10, 2016 at 1:58 PM Francesco Ariis <fa-ml at ariis.it> wrote:

> On Thu, Nov 10, 2016 at 07:44:17PM +0100, sasa bogicevic wrote:
> > Hi All,
> >
> > This is a small program
> >
> > [...]
>
> Hey Sasa,
> If we put this into ghci
>
>     λ> :t formatDateString $ timeFromString _
>
> the "hole" tells us we need something of type String, but `getDateString`
> is not!
>
>     λ> :t getDateString
>     getDateString :: IO UTCTime
>
> That means you have to bind it inside a `do` block (or use >>=).
> Ask for more if I was not clear!
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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From toad3k at gmail.com  Thu Nov 10 19:23:36 2016
From: toad3k at gmail.com (David McBride)
Date: Thu, 10 Nov 2016 14:23:36 -0500
Subject: [Haskell-beginners] OI UTCTime to String
In-Reply-To: <7085A8E2-7469-440C-BD04-747A056008B5@gmail.com>
References: <7085A8E2-7469-440C-BD04-747A056008B5@gmail.com>
Message-ID: <CAN+Tr402tEBE-qHXRzdjxcfGrCBibnrcBf_Tq-cHAMzjMbscNw@mail.gmail.com>

It looks like you are trying to get time in UTC, then figuring out what
date it is?  You should be able to get the answer you are looking for with

getFormattedDate = do
  utc <- getCurrentTime
  return $ formatTime defaultTimeLocale "%m/%d/%Y" utc

Just keep in mind that that is the date in UTC.  Not in your local time
zone and it ignores daylight savings time.  To get it in your time you'll
have to replace getCurrentTime with getZonedTime.

On Thu, Nov 10, 2016 at 1:44 PM, sasa bogicevic <brutallesale at gmail.com>
wrote:

> Hi All,
>
> This is a small program
>
> {-# LANGUAGE OverloadedStrings #-}
> module Main where
>
> import           Control.Monad.IO.Class     (liftIO)
> import qualified Data.ByteString.Lazy.Char8 as L
> import           Data.Time
> import           Network                    (withSocketsDo)
> import           Network.HTTP.Conduit
>
>
> createRequestData today = [("index:brKursneListe",""),
>  ("index:year","2016"),
>  ("index:inputCalendar1", today),
>  ("index:vrsta","3"),
>  ("index:prikaz","0"),
>  ("index:buttonShow","Prikazi")]
>
>
> timeFromString  s = parseTimeOrError True defaultTimeLocale "%d %b %Y
> %l:%M %p" s
>
> formatDateString time = formatTime defaultTimeLocale "%m/%d/%Y" time
>
> getDateString = getCurrentTime
>
> getFormatedDate  = formatDateString $ timeFromString getDateString
>
> main = do
>         print $ getFormatedDate
>
>
> And here is my error
>
> main.hs:25:54: error:
>    • Couldn't match type ‘IO UTCTime’ with ‘[Char]’
>      Expected type: String
>        Actual type: IO UTCTime
>    • In the first argument of ‘timeFromString’, namely ‘getDateString’
>      In the second argument of ‘($)’, namely
>        ‘timeFromString getDateString’
>      In the expression: formatDateString $ timeFromString getDateString
>
> Thanks!
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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From brutallesale at gmail.com  Thu Nov 10 20:44:37 2016
From: brutallesale at gmail.com (sasa bogicevic)
Date: Thu, 10 Nov 2016 21:44:37 +0100
Subject: [Haskell-beginners] OI UTCTime to String
In-Reply-To: <CAN+Tr402tEBE-qHXRzdjxcfGrCBibnrcBf_Tq-cHAMzjMbscNw@mail.gmail.com>
References: <7085A8E2-7469-440C-BD04-747A056008B5@gmail.com>
 <CAN+Tr402tEBE-qHXRzdjxcfGrCBibnrcBf_Tq-cHAMzjMbscNw@mail.gmail.com>
Message-ID: <69791B07-41A4-4397-96DB-469E42C3459C@gmail.com>

Thanks guys!
Didn't expect this much help so fast, great community!
I think my main problem was that I was constantly trying to print the result for my formatted date string which was of type IO String (at some point)
I just learned that to print IO you need to bind it something like this
 
main =  getFormattedDate >>= putStrLn

Thanks a lot, You rock!




> On Nov 10, 2016, at 20:23, David McBride <toad3k at gmail.com> wrote:
> 
> It looks like you are trying to get time in UTC, then figuring out what date it is?  You should be able to get the answer you are looking for with
> 
> getFormattedDate = do
>   utc <- getCurrentTime
>   return $ formatTime defaultTimeLocale "%m/%d/%Y" utc
> 
> Just keep in mind that that is the date in UTC.  Not in your local time zone and it ignores daylight savings time.  To get it in your time you'll have to replace getCurrentTime with getZonedTime.
> 
> On Thu, Nov 10, 2016 at 1:44 PM, sasa bogicevic <brutallesale at gmail.com> wrote:
> Hi All,
> 
> This is a small program
> 
> {-# LANGUAGE OverloadedStrings #-}
> module Main where
> 
> import           Control.Monad.IO.Class     (liftIO)
> import qualified Data.ByteString.Lazy.Char8 as L
> import           Data.Time
> import           Network                    (withSocketsDo)
> import           Network.HTTP.Conduit
> 
> 
> createRequestData today = [("index:brKursneListe",""),
>  ("index:year","2016"),
>  ("index:inputCalendar1", today),
>  ("index:vrsta","3"),
>  ("index:prikaz","0"),
>  ("index:buttonShow","Prikazi")]
> 
> 
> timeFromString  s = parseTimeOrError True defaultTimeLocale "%d %b %Y %l:%M %p" s
> 
> formatDateString time = formatTime defaultTimeLocale "%m/%d/%Y" time
> 
> getDateString = getCurrentTime
> 
> getFormatedDate  = formatDateString $ timeFromString getDateString
> 
> main = do
>         print $ getFormatedDate
> 
> 
> And here is my error
> 
> main.hs:25:54: error:
>    • Couldn't match type ‘IO UTCTime’ with ‘[Char]’
>      Expected type: String
>        Actual type: IO UTCTime
>    • In the first argument of ‘timeFromString’, namely ‘getDateString’
>      In the second argument of ‘($)’, namely
>        ‘timeFromString getDateString’
>      In the expression: formatDateString $ timeFromString getDateString
> 
> Thanks!
> 
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
> 
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners


From skippy_lou at hotmail.com  Sat Nov 12 20:20:19 2016
From: skippy_lou at hotmail.com (Lawrence Wickert)
Date: Sat, 12 Nov 2016 20:20:19 +0000
Subject: [Haskell-beginners] Equivalence (or not) of lists
Message-ID: <CO1PR14MB10168FDC114706981643775EEEBA0@CO1PR14MB1016.namprd14.prod.outlook.com>

Hello all,

I am a rank beginner to functional languages.  Working through Lipovaca's book, up to Chapter 3.

Ok, setup this function in editor and compiled:

length' :: (Num b) => [a] -> b
length' [] = 0
length' (_:xs) = 1 + length' xs


skippy at skippy:~$ ghci
GHCi, version 7.10.3: http://www.haskell.org/ghc/  :? for help
Prelude> :l baby
[1 of 1] Compiling Main             ( baby.hs, interpreted )
Ok, modules loaded: Main.
*Main> length' [1,2,3]
3
*Main> 1:2:3:[]
[1,2,3]
*Main> length' 1:2:3:[]

<interactive>:5:9:
    Could not deduce (Num [a0]) arising from the literal '1'
    from the context (Num a)
      bound by the inferred type of it :: Num a => [a]
      at <interactive>:5:1-16
    The type variable 'a0' is ambiguous
    In the first argument of 'length'', namely '1'
    In the first argument of '(:)', namely 'length' 1'
    In the expression: length' 1 : 2 : 3 : []
*Main>


Obviously, there is something I don't understand about the apparent non-equivalence of the lists [1,2,3] and 1:2:3:[]I am guessing that the solution is contained in that error message but I can't quite decipher it.

Thanks for any help.


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From sylvain at haskus.fr  Sat Nov 12 20:30:07 2016
From: sylvain at haskus.fr (Sylvain Henry)
Date: Sat, 12 Nov 2016 21:30:07 +0100
Subject: [Haskell-beginners] Equivalence (or not) of lists
In-Reply-To: <CO1PR14MB10168FDC114706981643775EEEBA0@CO1PR14MB1016.namprd14.prod.outlook.com>
References: <CO1PR14MB10168FDC114706981643775EEEBA0@CO1PR14MB1016.namprd14.prod.outlook.com>
Message-ID: <c47bf925-cab3-bc1e-e07e-82a23d917be2@haskus.fr>

Hi,


 > length' 1:2:3:[]

is equivalent to:


 > (length' 1):2:3:[]

hence the error.


Try:

 > length' (1:2:3:[])


Sylvain


On 12/11/2016 21:20, Lawrence Wickert wrote:
> Hello all,
>
> I am a rank beginner to functional languages.  Working through 
> Lipovaca's book, up to Chapter 3.
>
> Ok, setup this function in editor and compiled:
>
> length' :: (Num b) => [a] -> b
> length' [] = 0
> length' (_:xs) = 1 + length' xs
>
>
> skippy at skippy:~$ ghci
> GHCi, version 7.10.3: http://www.haskell.org/ghc/  :? for help
> Prelude> :l baby
> [1 of 1] Compiling Main             ( baby.hs, interpreted )
> Ok, modules loaded: Main.
> *Main> length' [1,2,3]
> 3
> *Main> 1:2:3:[]
> [1,2,3]
> *Main> length' 1:2:3:[]
>
> <interactive>:5:9:
>     Could not deduce (Num [a0]) arising from the literal ‘1’
>     from the context (Num a)
>       bound by the inferred type of it :: Num a => [a]
>       at <interactive>:5:1-16
>     The type variable ‘a0’ is ambiguous
>     In the first argument of ‘length'’, namely ‘1’
>     In the first argument of ‘(:)’, namely ‘length' 1’
>     In the expression: length' 1 : 2 : 3 : []
> *Main>
>
>
> Obviously, there is something I don't understand about the apparent 
> non-equivalence of the lists [1,2,3] and 1:2:3:[]I am guessing that 
> the solution is contained in that error message but I can't quite 
> decipher it.
>
> Thanks for any help.
>
>
>
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners

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From fa-ml at ariis.it  Sat Nov 12 20:27:21 2016
From: fa-ml at ariis.it (Francesco Ariis)
Date: Sat, 12 Nov 2016 21:27:21 +0100
Subject: [Haskell-beginners] Equivalence (or not) of lists
In-Reply-To: <CO1PR14MB10168FDC114706981643775EEEBA0@CO1PR14MB1016.namprd14.prod.outlook.com>
References: <CO1PR14MB10168FDC114706981643775EEEBA0@CO1PR14MB1016.namprd14.prod.outlook.com>
Message-ID: <20161112202346.GA2465@casa.casa>

On Sat, Nov 12, 2016 at 08:20:19PM +0000, Lawrence Wickert wrote:
> Hello all,
> 
> I am a rank beginner to functional languages.  Working through
> Lipovaca's book, up to Chapter 3.
> 
> [...]
>
> *Main> length' 1:2:3:[]

Hello Lawrence,
    remember that function application has precedence over operators!

So writing:

    *Main> length' 1:2:3:[]

is equivalent to writing

    *Main> (length' 1) :2:3:[]

(which is not what you want). If you add parentheses, your expression
works again!

    *Main> length' (1:2:3:[])

From fa-ml at ariis.it  Sat Nov 12 20:29:22 2016
From: fa-ml at ariis.it (Francesco Ariis)
Date: Sat, 12 Nov 2016 21:29:22 +0100
Subject: [Haskell-beginners] Equivalence (or not) of lists
In-Reply-To: <CO1PR14MB10168FDC114706981643775EEEBA0@CO1PR14MB1016.namprd14.prod.outlook.com>
References: <CO1PR14MB10168FDC114706981643775EEEBA0@CO1PR14MB1016.namprd14.prod.outlook.com>
Message-ID: <20161112202346.GA2465@casa.casa>

On Sat, Nov 12, 2016 at 08:20:19PM +0000, Lawrence Wickert wrote:
> Hello all,
> 
> I am a rank beginner to functional languages.  Working through
> Lipovaca's book, up to Chapter 3.
> 
> [...]
>
> *Main> length' 1:2:3:[]

Hello Lawrence,
    remember that function application has precedence over operators!

So writing:

    *Main> length' 1:2:3:[]

is equivalent to writing

    *Main> (length' 1) :2:3:[]

(which is not what you want). If you add parentheses, your expression
works again!

    *Main> length' (1:2:3:[])

From skippy_lou at hotmail.com  Sat Nov 12 20:38:37 2016
From: skippy_lou at hotmail.com (Lawrence Wickert)
Date: Sat, 12 Nov 2016 20:38:37 +0000
Subject: [Haskell-beginners] Equivalence (or not) of lists
Message-ID: <CO1PR14MB101622ACDDA51A0F18CA7E04EEBA0@CO1PR14MB1016.namprd14.prod.outlook.com>

Thanks, Sylvain.  That works and I think I understand the difference now.

Larry

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From jan.brusch at gmail.com  Sat Nov 12 21:43:13 2016
From: jan.brusch at gmail.com (Jan Brusch)
Date: Sat, 12 Nov 2016 22:43:13 +0100
Subject: [Haskell-beginners] Request for Code Review: Dice Game Distribution
Message-ID: <CAOSrD+4eikSnvg5YSwWdMzOkqRM0WT-tX5D1S6FrNOK7BU8dDg@mail.gmail.com>

Hi,

I'm currently learning Haskell and as a first project I wrote a little
helper for a dice game. It's very short. Nonetheless I would really
appreciate a little Code Review or any other input.

The Game: Each player writes down the numbers from 1 to 42. Each turn you
roll 3 dice (6-sided). The rolling player can cross of any one number that
he can construct from the three dice using the math operators +, -, *, /.
First player to cross off all numbers wins.

The Helper: Calculates the reachable numbers for each dice roll. It the
aggregates a count for each number, from how many dice rolls it can be
reached. E.g.: There are 216 possible dice rolls (6^3), the number 2 can be
reached form 171 of them. The helper gives out the data in JSON format that
can be read by NVD3 to be displayed in a browser. The graph helps you to
make a decision on which number you should prefer to cross off with your
current roll.

The Code: http://lpaste.net/338358

The Graph: http://imgur.com/a/NSDT8


Looking forward to any feedback and thanks in advance
Jan
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From laiboonh at gmail.com  Mon Nov 14 02:15:23 2016
From: laiboonh at gmail.com (Lai Boon Hui)
Date: Mon, 14 Nov 2016 10:15:23 +0800
Subject: [Haskell-beginners] How to tell haskell that 'a' is 'a' ?
Message-ID: <CAJdQggn8_8Wa7uvr2+0CWazZdeK+MGLKRh1PnUWOWOmNe+S8jw@mail.gmail.com>

Hi all,

skips :: [a] -> [[a]]
skips xs = go 1 [] where
  go :: Int -> [[a]] -> [[a]] *-- Compiles if i remove this line*
  go n acc
    | n > (length xs) = acc
    | n == 1 = xs : (go (n+1) acc)
    | n < 1 = []
    | otherwise = (everyN n xs) : (go (n+1) acc)

everyN :: Int -> [a] -> [a]
everyN n xs =
  case (drop (n-1) xs) of
    y:ys -> y : (everyN n ys)
    [] -> []

How can i tell haskell compiler that a is the sub program if the same as a
in the main program?


-- 
Best Regards,
Boon Hui
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From sylvain at haskus.fr  Mon Nov 14 02:26:27 2016
From: sylvain at haskus.fr (Sylvain Henry)
Date: Mon, 14 Nov 2016 03:26:27 +0100
Subject: [Haskell-beginners] How to tell haskell that 'a' is 'a' ?
In-Reply-To: <CAJdQggn8_8Wa7uvr2+0CWazZdeK+MGLKRh1PnUWOWOmNe+S8jw@mail.gmail.com>
References: <CAJdQggn8_8Wa7uvr2+0CWazZdeK+MGLKRh1PnUWOWOmNe+S8jw@mail.gmail.com>
Message-ID: <3178e490-9884-676d-843a-162e29288b59@haskus.fr>

Hi,

Use ScopedTypeVariables and forall:

{-# LANGUAGE ScopedTypeVariables #-}

skips :: forall a. [a] -> [[a]]
skips xs = go 1 [] where
    go :: Int -> [[a]] -> [[a]]
*   ...*

Sylvain

On 14/11/2016 03:15, Lai Boon Hui wrote:
> Hi all,
>
> skips :: [a] -> [[a]]
> skips xs = go 1 [] where
>   go :: Int -> [[a]] -> [[a]] *-- Compiles if i remove this line*
>   go n acc
>     | n > (length xs) = acc
>     | n == 1 = xs : (go (n+1) acc)
>     | n < 1 = []
>     | otherwise = (everyN n xs) : (go (n+1) acc)
>
> everyN :: Int -> [a] -> [a]
> everyN n xs =
>   case (drop (n-1) xs) of
>     y:ys -> y : (everyN n ys)
>     [] -> []
>
> How can i tell haskell compiler that a is the sub program if the same 
> as a in the main program?
>
>
> -- 
> Best Regards,
> Boon Hui
>
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners

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From csasarak at mailbox.org  Mon Nov 14 02:58:27 2016
From: csasarak at mailbox.org (Chris Sasarak)
Date: Sun, 13 Nov 2016 21:58:27 -0500
Subject: [Haskell-beginners] Equivalence (or not) of lists
In-Reply-To: <20161112202346.GA2465@casa.casa>
References: <CO1PR14MB10168FDC114706981643775EEEBA0@CO1PR14MB1016.namprd14.prod.outlook.com>
 <20161112202346.GA2465@casa.casa>
Message-ID: <87fumuwywc.fsf@mailbox.org>


In this case it's not too bad adding parens to make:

   length' (1:2:3:[])

But in the future sometimes it can get harder, so we have a handy
function '$' which is just function application, but it has the lowest
precedence. What this means is everything on its right side is evaluated
and then applied to the function on its left. Your code would look like
this:

    length' $ 1:2:3:[]
    
In some cases this can be more readable.

Best,
Chris

Francesco Ariis writes:

> On Sat, Nov 12, 2016 at 08:20:19PM +0000, Lawrence Wickert wrote:
>> Hello all,
>> 
>> I am a rank beginner to functional languages.  Working through
>> Lipovaca's book, up to Chapter 3.
>> 
>> [...]
>>
>> *Main> length' 1:2:3:[]
>
> Hello Lawrence,
>     remember that function application has precedence over operators!
>
> So writing:
>
>     *Main> length' 1:2:3:[]
>
> is equivalent to writing
>
>     *Main> (length' 1) :2:3:[]
>
> (which is not what you want). If you add parentheses, your expression
> works again!
>
>     *Main> length' (1:2:3:[])
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners


From clever97 at gmail.com  Thu Nov 17 21:52:14 2016
From: clever97 at gmail.com (Cleverson Casarin Uliana)
Date: Thu, 17 Nov 2016 19:52:14 -0200
Subject: [Haskell-beginners] Setting up WXHaskell on the 8.0.1 platform?
Message-ID: <2d6245ff-7dcc-2105-2d7d-199e7bb11514@gmail.com>

Hello all, I've sent this to the WXHaskell list, but no answers. Please 
what is the recommended way to set up WXWidgets and WXHaskell for the 
8.0.1 Haskell Platform on Windows? I tried using the Achelanne 
installer, but it gives errors apparently related to packages versions 
incompatibilities.

Thanks,
Cleverson

From briand at aracnet.com  Fri Nov 25 05:46:13 2016
From: briand at aracnet.com (briand at aracnet.com)
Date: Thu, 24 Nov 2016 21:46:13 -0800
Subject: [Haskell-beginners] pattern matching on a common element
Message-ID: <20161124214613.576a0912@basalt.deldotd.com>

Here's what I'm doing:

data X = A1 String Double | A2 String Int | A3 String Double Int

name c =
  case c of
    A1 name _ -> name
    A2 name _ -> name
    A3 name _ _ -> name

I'm sure there's a better way...

From rahulmutt at gmail.com  Fri Nov 25 06:36:06 2016
From: rahulmutt at gmail.com (Rahul Muttineni)
Date: Fri, 25 Nov 2016 12:06:06 +0530
Subject: [Haskell-beginners] pattern matching on a common element
In-Reply-To: <20161124214613.576a0912@basalt.deldotd.com>
References: <20161124214613.576a0912@basalt.deldotd.com>
Message-ID: <CANij+eR5LV9fn_3pdu_QBBrbf5equOraOH7+u0_zjGN1mxjzeA@mail.gmail.com>

data X =
  A1 { name :: String, d :: Double}
| A2 { name :: String, i :: Int}
| A3 { name :: String, d1 :: Double, i1 :: Int}

Now you can use `name` directly to get the string component of the
different variants.

Hope that helps!
Rahul

On Fri, Nov 25, 2016 at 11:16 AM, <briand at aracnet.com> wrote:

> Here's what I'm doing:
>
> data X = A1 String Double | A2 String Int | A3 String Double Int
>
> name c =
>   case c of
>     A1 name _ -> name
>     A2 name _ -> name
>     A3 name _ _ -> name
>
> I'm sure there's a better way...
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>



-- 
Rahul Muttineni
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From briand at aracnet.com  Fri Nov 25 07:08:02 2016
From: briand at aracnet.com (briand at aracnet.com)
Date: Thu, 24 Nov 2016 23:08:02 -0800
Subject: [Haskell-beginners] pattern matching on a common element
In-Reply-To: <CANij+eR5LV9fn_3pdu_QBBrbf5equOraOH7+u0_zjGN1mxjzeA@mail.gmail.com>
References: <20161124214613.576a0912@basalt.deldotd.com>
 <CANij+eR5LV9fn_3pdu_QBBrbf5equOraOH7+u0_zjGN1mxjzeA@mail.gmail.com>
Message-ID: <20161124230802.2ec92e72@basalt.deldotd.com>

On Fri, 25 Nov 2016 12:06:06 +0530
Rahul Muttineni <rahulmutt at gmail.com> wrote:

> data X =
>   A1 { name :: String, d :: Double}
> | A2 { name :: String, i :: Int}
> | A3 { name :: String, d1 :: Double, i1 :: Int}
> 
> Now you can use `name` directly to get the string component of the
> different variants.
> 
> Hope that helps!

oops, i forgot to mention.

i'd like to be able to write my code;

x =  [ A1 "a1" 2.0, A2 "a2" 3 ]

etc... to save myself a lot of typing.



From jeffbrown.the at gmail.com  Fri Nov 25 07:09:26 2016
From: jeffbrown.the at gmail.com (Jeffrey Brown)
Date: Thu, 24 Nov 2016 23:09:26 -0800
Subject: [Haskell-beginners] pattern matching on a common element
In-Reply-To: <20161124230802.2ec92e72@basalt.deldotd.com>
References: <20161124214613.576a0912@basalt.deldotd.com>
 <CANij+eR5LV9fn_3pdu_QBBrbf5equOraOH7+u0_zjGN1mxjzeA@mail.gmail.com>
 <20161124230802.2ec92e72@basalt.deldotd.com>
Message-ID: <CAEc4Ma3+QDGbuwsuSs6dp0uoAjE71fP8NkN3qsRMnxyAHvuibQ@mail.gmail.com>

You still can! Using Rahul's solution, that is.

On Thu, Nov 24, 2016 at 11:08 PM, <briand at aracnet.com> wrote:

> On Fri, 25 Nov 2016 12:06:06 +0530
> Rahul Muttineni <rahulmutt at gmail.com> wrote:
>
> > data X =
> >   A1 { name :: String, d :: Double}
> > | A2 { name :: String, i :: Int}
> > | A3 { name :: String, d1 :: Double, i1 :: Int}
> >
> > Now you can use `name` directly to get the string component of the
> > different variants.
> >
> > Hope that helps!
>
> oops, i forgot to mention.
>
> i'd like to be able to write my code;
>
> x =  [ A1 "a1" 2.0, A2 "a2" 3 ]
>
> etc... to save myself a lot of typing.
>
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>



-- 
Jeff Brown | Jeffrey Benjamin Brown
Website <https://msu.edu/~brown202/>   |   Facebook
<https://www.facebook.com/mejeff.younotjeff>   |   LinkedIn
<https://www.linkedin.com/in/jeffreybenjaminbrown>(I often miss messages
here)   |   Github <https://github.com/jeffreybenjaminbrown>
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From briand at aracnet.com  Fri Nov 25 07:34:10 2016
From: briand at aracnet.com (briand at aracnet.com)
Date: Thu, 24 Nov 2016 23:34:10 -0800
Subject: [Haskell-beginners] pattern matching on a common element
In-Reply-To: <CAEc4Ma3+QDGbuwsuSs6dp0uoAjE71fP8NkN3qsRMnxyAHvuibQ@mail.gmail.com>
References: <20161124214613.576a0912@basalt.deldotd.com>
 <CANij+eR5LV9fn_3pdu_QBBrbf5equOraOH7+u0_zjGN1mxjzeA@mail.gmail.com>
 <20161124230802.2ec92e72@basalt.deldotd.com>
 <CAEc4Ma3+QDGbuwsuSs6dp0uoAjE71fP8NkN3qsRMnxyAHvuibQ@mail.gmail.com>
Message-ID: <20161124233410.35ff48aa@basalt.deldotd.com>

On Thu, 24 Nov 2016 23:09:26 -0800
Jeffrey Brown <jeffbrown.the at gmail.com> wrote:

> You still can! Using Rahul's solution, that is.

but wouldn't i have to write
 
  A1 {name="a1", d="2.0}
  A2 {name="a2", i=2}

etc...

?

That would be ok for these simple examples, but for my actual code the field names would not be just 1 or 2 characters.


Brian

> 
> On Thu, Nov 24, 2016 at 11:08 PM, <briand at aracnet.com> wrote:
> 
> > On Fri, 25 Nov 2016 12:06:06 +0530
> > Rahul Muttineni <rahulmutt at gmail.com> wrote:
> >  
> > > data X =
> > >   A1 { name :: String, d :: Double}
> > > | A2 { name :: String, i :: Int}
> > > | A3 { name :: String, d1 :: Double, i1 :: Int}
> > >
> > > Now you can use `name` directly to get the string component of the
> > > different variants.
> > >
> > > Hope that helps!  
> >
> > oops, i forgot to mention.
> >
> > i'd like to be able to write my code;
> >
> > x =  [ A1 "a1" 2.0, A2 "a2" 3 ]
> >
> > etc... to save myself a lot of typing.
> >
> >
> > _______________________________________________
> > Beginners mailing list
> > Beginners at haskell.org
> > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
> >  
> 
> 
> 


From rein.henrichs at gmail.com  Fri Nov 25 08:41:46 2016
From: rein.henrichs at gmail.com (Rein Henrichs)
Date: Fri, 25 Nov 2016 08:41:46 +0000
Subject: [Haskell-beginners] pattern matching on a common element
In-Reply-To: <20161124233410.35ff48aa@basalt.deldotd.com>
References: <20161124214613.576a0912@basalt.deldotd.com>
 <CANij+eR5LV9fn_3pdu_QBBrbf5equOraOH7+u0_zjGN1mxjzeA@mail.gmail.com>
 <20161124230802.2ec92e72@basalt.deldotd.com>
 <CAEc4Ma3+QDGbuwsuSs6dp0uoAjE71fP8NkN3qsRMnxyAHvuibQ@mail.gmail.com>
 <20161124233410.35ff48aa@basalt.deldotd.com>
Message-ID: <CAJp6G8wRzPZiuid4ncaCV1u-UHUDgoqMmVfRnEzdwPCwfbEMBQ@mail.gmail.com>

No, you would not. Record syntax is an addition to, not a replacement for,
the form you want to use.

On Thu, Nov 24, 2016 at 11:34 PM <briand at aracnet.com> wrote:

On Thu, 24 Nov 2016 23:09:26 -0800
Jeffrey Brown <jeffbrown.the at gmail.com> wrote:

> You still can! Using Rahul's solution, that is.

but wouldn't i have to write

  A1 {name="a1", d="2.0}
  A2 {name="a2", i=2}

etc...

?

That would be ok for these simple examples, but for my actual code the
field names would not be just 1 or 2 characters.


Brian

>
> On Thu, Nov 24, 2016 at 11:08 PM, <briand at aracnet.com> wrote:
>
> > On Fri, 25 Nov 2016 12:06:06 +0530
> > Rahul Muttineni <rahulmutt at gmail.com> wrote:
> >
> > > data X =
> > >   A1 { name :: String, d :: Double}
> > > | A2 { name :: String, i :: Int}
> > > | A3 { name :: String, d1 :: Double, i1 :: Int}
> > >
> > > Now you can use `name` directly to get the string component of the
> > > different variants.
> > >
> > > Hope that helps!
> >
> > oops, i forgot to mention.
> >
> > i'd like to be able to write my code;
> >
> > x =  [ A1 "a1" 2.0, A2 "a2" 3 ]
> >
> > etc... to save myself a lot of typing.
> >
> >
> > _______________________________________________
> > Beginners mailing list
> > Beginners at haskell.org
> > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
> >
>
>
>

_______________________________________________
Beginners mailing list
Beginners at haskell.org
http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
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From daniel.trstenjak at gmail.com  Fri Nov 25 09:19:14 2016
From: daniel.trstenjak at gmail.com (Daniel Trstenjak)
Date: Fri, 25 Nov 2016 10:19:14 +0100
Subject: [Haskell-beginners] pattern matching on a common element
In-Reply-To: <CANij+eR5LV9fn_3pdu_QBBrbf5equOraOH7+u0_zjGN1mxjzeA@mail.gmail.com>
References: <20161124214613.576a0912@basalt.deldotd.com>
 <CANij+eR5LV9fn_3pdu_QBBrbf5equOraOH7+u0_zjGN1mxjzeA@mail.gmail.com>
Message-ID: <20161125091914.GA9587@octa>


Hi Rahul,

On Fri, Nov 25, 2016 at 12:06:06PM +0530, Rahul Muttineni wrote:
> data X =
>   A1 { name :: String, d :: Double}
> | A2 { name :: String, i :: Int}
> | A3 { name :: String, d1 :: Double, i1 :: Int}
> 
> Now you can use `name` directly to get the string component of the different
> variants.

It's not recommended to mix record syntax and ADTs, because you
can get runtime errors that the compiler can't catch during compile
time, like calling:

   i (A1 "foo" 3.2)

If you're having the same field in all variants, then an
other approach might be better:

   data A = Ai Int | Ad Double | Aid Int Double

   data X = X { name :: String, a :: A }

Greetings,
Daniel

From briand at aracnet.com  Fri Nov 25 16:08:35 2016
From: briand at aracnet.com (briand at aracnet.com)
Date: Fri, 25 Nov 2016 08:08:35 -0800
Subject: [Haskell-beginners] pattern matching on a common element
In-Reply-To: <CAJp6G8wRzPZiuid4ncaCV1u-UHUDgoqMmVfRnEzdwPCwfbEMBQ@mail.gmail.com>
References: <20161124214613.576a0912@basalt.deldotd.com>
 <CANij+eR5LV9fn_3pdu_QBBrbf5equOraOH7+u0_zjGN1mxjzeA@mail.gmail.com>
 <20161124230802.2ec92e72@basalt.deldotd.com>
 <CAEc4Ma3+QDGbuwsuSs6dp0uoAjE71fP8NkN3qsRMnxyAHvuibQ@mail.gmail.com>
 <20161124233410.35ff48aa@basalt.deldotd.com>
 <CAJp6G8wRzPZiuid4ncaCV1u-UHUDgoqMmVfRnEzdwPCwfbEMBQ@mail.gmail.com>
Message-ID: <20161125080835.4446131c@basalt.deldotd.com>

On Fri, 25 Nov 2016 08:41:46 +0000
Rein Henrichs <rein.henrichs at gmail.com> wrote:

> No, you would not. Record syntax is an addition to, not a replacement for,
> the form you want to use.
> 

oh, I see.  I had tried 

 A1 { "a1" 2.0 }

instead of

  A1 ("a1" 2.0)


Brian

From briand at aracnet.com  Fri Nov 25 16:20:29 2016
From: briand at aracnet.com (briand at aracnet.com)
Date: Fri, 25 Nov 2016 08:20:29 -0800
Subject: [Haskell-beginners] pattern matching on a common element
In-Reply-To: <20161125091914.GA9587@octa>
References: <20161124214613.576a0912@basalt.deldotd.com>
 <CANij+eR5LV9fn_3pdu_QBBrbf5equOraOH7+u0_zjGN1mxjzeA@mail.gmail.com>
 <20161125091914.GA9587@octa>
Message-ID: <20161125082029.2ca609a7@basalt.deldotd.com>

On Fri, 25 Nov 2016 10:19:14 +0100
Daniel Trstenjak <daniel.trstenjak at gmail.com> wrote:

> Hi Rahul,
> 
> On Fri, Nov 25, 2016 at 12:06:06PM +0530, Rahul Muttineni wrote:
> > data X =
> >   A1 { name :: String, d :: Double}
> > | A2 { name :: String, i :: Int}
> > | A3 { name :: String, d1 :: Double, i1 :: Int}
> > 
> > Now you can use `name` directly to get the string component of the different
> > variants.  
> 
> It's not recommended to mix record syntax and ADTs, because you
> can get runtime errors that the compiler can't catch during compile
> time, like calling:
> 
>    i (A1 "foo" 3.2)
> 

agreed.  I'm doing this as a form of shorthand instead of creating a text file based input and parsing it.  Having any sort of type checking is an advantage.

> If you're having the same field in all variants, then an
> other approach might be better:
> 
>    data A = Ai Int | Ad Double | Aid Int Double
> 
>    data X = X { name :: String, a :: A }
> 

yes, that would be better.

interestingly in my journeys through the intertubes I have not found a single mention of using the "()" syntax in place of the "{fieldname=value, ...}" syntax as the generator.


Brian


From daniel.trstenjak at gmail.com  Fri Nov 25 17:18:21 2016
From: daniel.trstenjak at gmail.com (Daniel Trstenjak)
Date: Fri, 25 Nov 2016 18:18:21 +0100
Subject: [Haskell-beginners] pattern matching on a common element
In-Reply-To: <20161125082029.2ca609a7@basalt.deldotd.com>
References: <20161124214613.576a0912@basalt.deldotd.com>
 <CANij+eR5LV9fn_3pdu_QBBrbf5equOraOH7+u0_zjGN1mxjzeA@mail.gmail.com>
 <20161125091914.GA9587@octa>
 <20161125082029.2ca609a7@basalt.deldotd.com>
Message-ID: <20161125171821.GA4138@octa>


Hi Brian,

> interestingly in my journeys through the intertubes I have not found a
> single mention of using the "()" syntax in place of the
> "{fieldname=value, ...}" syntax as the generator.

The '()' isn't part of the 'data constructor' (the usual term for A1/A2/A3),
but sometimes needed to help the compiler to make an unambiguous parsing of the expression.

These are all valid expressions:

    i $ A1 "foo" 3.2   -- '$' is often used to get rid of parentheses

    let a1 = A1 "foo" 3.2 in i a1

Greetings,
Daniel

From briand at aracnet.com  Fri Nov 25 20:50:01 2016
From: briand at aracnet.com (briand at aracnet.com)
Date: Fri, 25 Nov 2016 12:50:01 -0800
Subject: [Haskell-beginners] pattern matching on a common element
In-Reply-To: <20161125171821.GA4138@octa>
References: <20161124214613.576a0912@basalt.deldotd.com>
 <CANij+eR5LV9fn_3pdu_QBBrbf5equOraOH7+u0_zjGN1mxjzeA@mail.gmail.com>
 <20161125091914.GA9587@octa>
 <20161125082029.2ca609a7@basalt.deldotd.com>
 <20161125171821.GA4138@octa>
Message-ID: <20161125125001.4e09cbc5@basalt.deldotd.com>

On Fri, 25 Nov 2016 18:18:21 +0100
Daniel Trstenjak <daniel.trstenjak at gmail.com> wrote:

> Hi Brian,
> 
> > interestingly in my journeys through the intertubes I have not found a
> > single mention of using the "()" syntax in place of the
> > "{fieldname=value, ...}" syntax as the generator.  
> 
> The '()' isn't part of the 'data constructor' (the usual term for A1/A2/A3),
> but sometimes needed to help the compiler to make an unambiguous parsing of the expression.
> 
> These are all valid expressions:
> 
>     i $ A1 "foo" 3.2   -- '$' is often used to get rid of parentheses
> 
>     let a1 = A1 "foo" 3.2 in i a1
> 

oh, i see. everything's a function.

thanks!


Brian

From newhoggy at gmail.com  Sun Nov 27 21:23:18 2016
From: newhoggy at gmail.com (John Ky)
Date: Sun, 27 Nov 2016 21:23:18 +0000
Subject: [Haskell-beginners] Real World Haskell: Deprecated Libraries
Message-ID: <CAMB4o-CufNTU7_rob23VEjsfjTyWLMVw=ijnGsujSSnMCXecgw@mail.gmail.com>

Hello Haskellers,

I have been working through the Real World Haskell chapter on Profiling and
Optimisation
<http://book.realworldhaskell.org/read/profiling-and-optimization.html>,
and got to the section *Advanced techniques: fusion*, where I encountered
some code using Data.Array.Vector from the deprecated library uvector.

Does anyone know how to rewrite this to not use deprecated libraries?

I have tried to use Data.Vector.Unboxed from vector, but my version
consumes a lot of memory.

The code I have is here:

https://github.com/haskell-works/hw-tutorial-performance/blob/master/hw-tutorial-performance-rwhe/Main.hs

With that code, I get “1831 MB total memory in use”, which is terrible

Build run steps I used were:

stack build --executable-profiling --library-profiling
--ghc-options="-fprof-auto -rtsopts -auto-all -caf-all -fforce-recomp"

time /Users/jky/wrk/haskell-works/hw-tutorial-performance/.stack-work/install/x86_64-osx/lts-7.10/8.0.1/bin/hw-tutorial-performance-rwhe
+RTS -sstderr -p -hy -RTS 1e7

I get very large numbers of allocations of Pair and Double.

There is also a very large upfront allocation ARR_WORDS, which I feared
would happen when using Data.Vector

Any help appreciated.

Cheers,

-John
​
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From newhoggy at gmail.com  Sun Nov 27 22:39:29 2016
From: newhoggy at gmail.com (John Ky)
Date: Sun, 27 Nov 2016 22:39:29 +0000
Subject: [Haskell-beginners] Real World Haskell: Deprecated Libraries
In-Reply-To: <CAMB4o-CufNTU7_rob23VEjsfjTyWLMVw=ijnGsujSSnMCXecgw@mail.gmail.com>
References: <CAMB4o-CufNTU7_rob23VEjsfjTyWLMVw=ijnGsujSSnMCXecgw@mail.gmail.com>
Message-ID: <CAMB4o-BBTe29LOv+yDB_J6sx5ST8cXoBYXXv9PY6dUbQy50Pag@mail.gmail.com>

It looks like Haskell stack's profile options are defeating stream fusion.

Anyone know a work-around?


On Mon, 28 Nov 2016 at 08:23 John Ky <newhoggy at gmail.com> wrote:

> Hello Haskellers,
>
> I have been working through the Real World Haskell chapter on Profiling
> and Optimisation
> <http://book.realworldhaskell.org/read/profiling-and-optimization.html>,
> and got to the section *Advanced techniques: fusion*, where I encountered
> some code using Data.Array.Vector from the deprecated library uvector.
>
> Does anyone know how to rewrite this to not use deprecated libraries?
>
> I have tried to use Data.Vector.Unboxed from vector, but my version
> consumes a lot of memory.
>
> The code I have is here:
>
>
> https://github.com/haskell-works/hw-tutorial-performance/blob/master/hw-tutorial-performance-rwhe/Main.hs
>
> With that code, I get “1831 MB total memory in use”, which is terrible
>
> Build run steps I used were:
>
> stack build --executable-profiling --library-profiling --ghc-options="-fprof-auto -rtsopts -auto-all -caf-all -fforce-recomp"
>
> time /Users/jky/wrk/haskell-works/hw-tutorial-performance/.stack-work/install/x86_64-osx/lts-7.10/8.0.1/bin/hw-tutorial-performance-rwhe +RTS -sstderr -p -hy -RTS 1e7
>
> I get very large numbers of allocations of Pair and Double.
>
> There is also a very large upfront allocation ARR_WORDS, which I feared
> would happen when using Data.Vector
>
> Any help appreciated.
>
> Cheers,
>
> -John
> ​
>
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From csasarak at mailbox.org  Sun Nov 27 23:08:07 2016
From: csasarak at mailbox.org (Christopher Sasarak)
Date: Sun, 27 Nov 2016 18:08:07 -0500
Subject: [Haskell-beginners] Setting up WXHaskell on the 8.0.1 platform?
In-Reply-To: <2d6245ff-7dcc-2105-2d7d-199e7bb11514@gmail.com>
References: <2d6245ff-7dcc-2105-2d7d-199e7bb11514@gmail.com>
Message-ID: <87polgttbc.fsf@mailbox.org>

I haven't set it up on windows before, but would you mind showing the
error message?

That would make it a lot easier to see exactly what the problem is.

-Chris

Cleverson Casarin Uliana writes:

> Hello all, I've sent this to the WXHaskell list, but no answers. Please 
> what is the recommended way to set up WXWidgets and WXHaskell for the 
> 8.0.1 Haskell Platform on Windows? I tried using the Achelanne 
> installer, but it gives errors apparently related to packages versions 
> incompatibilities.
>
> Thanks,
> Cleverson
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners


-- 

Best,
Chris

From bob at redivi.com  Mon Nov 28 00:57:20 2016
From: bob at redivi.com (Bob Ippolito)
Date: Sun, 27 Nov 2016 16:57:20 -0800
Subject: [Haskell-beginners] Real World Haskell: Deprecated Libraries
In-Reply-To: <CAMB4o-BBTe29LOv+yDB_J6sx5ST8cXoBYXXv9PY6dUbQy50Pag@mail.gmail.com>
References: <CAMB4o-CufNTU7_rob23VEjsfjTyWLMVw=ijnGsujSSnMCXecgw@mail.gmail.com>
 <CAMB4o-BBTe29LOv+yDB_J6sx5ST8cXoBYXXv9PY6dUbQy50Pag@mail.gmail.com>
Message-ID: <CACwMPm-kuZThJyt9y-2miosuj6f20RbKB2DTGuMJmJb6nov-Jw@mail.gmail.com>

Try using foldl', usually that's the right thing to do for this kind of
data structure.

On Sun, Nov 27, 2016 at 2:39 PM, John Ky <newhoggy at gmail.com> wrote:

> It looks like Haskell stack's profile options are defeating stream fusion.
>
> Anyone know a work-around?
>
>
> On Mon, 28 Nov 2016 at 08:23 John Ky <newhoggy at gmail.com> wrote:
>
>> Hello Haskellers,
>>
>> I have been working through the Real World Haskell chapter on Profiling
>> and Optimisation
>> <http://book.realworldhaskell.org/read/profiling-and-optimization.html>,
>> and got to the section *Advanced techniques: fusion*, where I
>> encountered some code using Data.Array.Vector from the deprecated
>> library uvector.
>>
>> Does anyone know how to rewrite this to not use deprecated libraries?
>>
>> I have tried to use Data.Vector.Unboxed from vector, but my version
>> consumes a lot of memory.
>>
>> The code I have is here:
>>
>> https://github.com/haskell-works/hw-tutorial-performance/
>> blob/master/hw-tutorial-performance-rwhe/Main.hs
>>
>> With that code, I get “1831 MB total memory in use”, which is terrible
>>
>> Build run steps I used were:
>>
>> stack build --executable-profiling --library-profiling --ghc-options="-fprof-auto -rtsopts -auto-all -caf-all -fforce-recomp"
>>
>> time /Users/jky/wrk/haskell-works/hw-tutorial-performance/.stack-work/install/x86_64-osx/lts-7.10/8.0.1/bin/hw-tutorial-performance-rwhe +RTS -sstderr -p -hy -RTS 1e7
>>
>> I get very large numbers of allocations of Pair and Double.
>>
>> There is also a very large upfront allocation ARR_WORDS, which I feared
>> would happen when using Data.Vector
>>
>> Any help appreciated.
>>
>> Cheers,
>>
>> -John
>> ​
>>
>
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