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Today's Topics:
1. number formatting with locale (Dmitry Simonchik)
2. idiomatic haskell question (Tom Doris)
3. qtHaskell, ForeignPtr (Michael Mossey)
4. oops (Michael Mossey)
5. Re: oops (Peter Verswyvelen)
6. Re: qtHaskell, ForeignPtr (Daniel Fischer)
7. Re: idiomatic haskell question (Andrew Wagner)
----------------------------------------------------------------------
Message: 1
Date: Mon, 7 Sep 2009 13:05:39 +0400
From: Dmitry Simonchik <[email protected]>
Subject: [Haskell-beginners] number formatting with locale
To: [email protected]
Message-ID:
<[email protected]>
Content-Type: text/plain; charset="utf-8"
Hi all haskell lovers
I'm trying to print out Double in russian locale (we use "," as decimal
separator insetad of "."). I'm trying to set locale with
System.Locale.SetLocale like
setLocale LC_ALL $ Just "ru_RU.UTF-8"
this returns Just "ru_RU.UTF-8", so it seems that function call succeeded,
but when I call
show 20.2
it just prints 20.2 and not desired 20,2
Can anyone please help?
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Message: 2
Date: Mon, 7 Sep 2009 18:28:22 +0100
From: Tom Doris <[email protected]>
Subject: [Haskell-beginners] idiomatic haskell question
To: [email protected]
Message-ID:
<[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
Hi all, I've recently started using Haskell and am looking for some feedback
on code I've written; I sometimes feel that maybe I'm not doing things the
best way possible that Haskell allows, and maybe missing out on obvious
improvements in brevity or elegance. So here's a tic-tac-toe solver I wrote
that does basic min-max search of the entire tree (not efficient
algorithmically, but it's tictactoe so a blank board can be fully solved in
a few seconds). Also, if people have suggestions on how to change the
program to actually output the moves it would make, please let me know -
right now it just responds with 1 for a win for X, 0 for a draw, and -1 for
a win for O. And there are probably bugs!
Thanks in advance
import Data.List
data Box = Blank | X | O deriving (Eq, Show)
-- usage: call score with the board rows concatenated: score [Blank, Blank,
Blank, Blank, Blank, Blank, Blank, Blank, Blank]
-- or score [Blank, X, O, Blank, X, O, Blank, Blank, Blank]
-- score is 1 if X wins, 0 for draw, -1 for lose
score :: [Box] -> Int
score g | haveline X g = 1
| haveline O g = -1
| gridfull g = 0
| isxmove g = maximum (map score (makeallmoves X g))
| otherwise = minimum (map score (makeallmoves O g))
tolines :: [Box] -> [[Box]]
tolines [a1, a2, a3, b1, b2, b3, c1, c2, c3] = [ [a1,a2,a3], [b1,b2,b3],
[c1,c2,c3],
[a1,b1,c1], [a2,b2,c2],
[a3,b3,c3],
[a1,b2,c3], [a3,b2,c1] ]
haveline :: Box->[Box] -> Bool
haveline b g = any ([b,b,b]==) (tolines g)
gridfull :: [Box] -> Bool
gridfull g = not $ any (Blank==) g
isxmove :: [Box] -> Bool
isxmove g = let movecount = sum $ map (\b -> if b==Blank then 0 else 1) g
in mod movecount 2 == 0
isomove = not . isxmove
fl :: Box->[Box]->[Box]->[[Box]]
fl b xs (Blank:ys) = [xs ++ b:ys]
fl _ _ _ = []
makeallmoves :: Box->[Box]-> [[Box]]
makeallmoves b g = concat $ zipWith (fl b) (inits g) (tails g)
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Message: 3
Date: Mon, 7 Sep 2009 14:54:17 -0700 (PDT)
From: "Michael Mossey" <[email protected]>
Subject: [Haskell-beginners] qtHaskell, ForeignPtr
To: [email protected]
Message-ID:
<[email protected]>
Content-Type: text/plain;charset=iso-8859-1
I'm trying to learn qtHaskell, an interface to the Qt GUI library. I am
fairly new to Haskell, but have used Qt for a long time, so I thought I
could probably reasonably attempt to grok qtHaskell at this point.
My main question is: anyone recommended a good explanation of the foreign
function or foreign pointer interface?
My immediate question is that I was poking through the Qtc docs, and saw
this:
Documentation
data Object a
Constructors
QObject !(ForeignPtr a)
I am not sure how Haddock works. Is this telling me that an Object
constructor takes one argument, which is of type QObject, where QObject is
a type constructor that takes !(ForeignPtr a)? Or is this saying it takes
two arguments, a QObject and a !(ForeignPtr a). That latter makes more
sense I guess. What does the ! mean?
Thanks,
Mike
------------------------------
Message: 4
Date: Mon, 7 Sep 2009 14:57:20 -0700 (PDT)
From: "Michael Mossey" <[email protected]>
Subject: [Haskell-beginners] oops
To: [email protected]
Message-ID:
<[email protected]>
Content-Type: text/plain;charset=iso-8859-1
I'm sorry, I just noticed one of my prior questions was pretty silly. The
second Object is the name of the type constructor. I realized that now. I
was just fooled by the layout of Haddock and got temporarily confused.
However, I'm still interested in learning more about what the ! means, and
where I can learn about ForeignPtr (maybe a short tutorial to start).
Thanks,
Mike
------------------------------
Message: 5
Date: Tue, 8 Sep 2009 00:14:28 +0200
From: Peter Verswyvelen <[email protected]>
Subject: Re: [Haskell-beginners] oops
To: Michael Mossey <[email protected]>
Cc: [email protected]
Message-ID:
<[email protected]>
Content-Type: text/plain; charset=ISO-8859-1
About the !
These might help
http://en.wikibooks.org/wiki/Haskell/Laziness
http://en.wikibooks.org/wiki/Haskell/Graph_reduction
On Mon, Sep 7, 2009 at 11:57 PM, Michael Mossey<[email protected]> wrote:
> I'm sorry, I just noticed one of my prior questions was pretty silly. The
> second Object is the name of the type constructor. I realized that now. I
> was just fooled by the layout of Haddock and got temporarily confused.
> However, I'm still interested in learning more about what the ! means, and
> where I can learn about ForeignPtr (maybe a short tutorial to start).
>
> Thanks,
> Mike
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
>
------------------------------
Message: 6
Date: Tue, 8 Sep 2009 00:36:00 +0200
From: Daniel Fischer <[email protected]>
Subject: Re: [Haskell-beginners] qtHaskell, ForeignPtr
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
Am Montag 07 September 2009 23:54:17 schrieb Michael Mossey:
> I'm trying to learn qtHaskell, an interface to the Qt GUI library. I am
> fairly new to Haskell, but have used Qt for a long time, so I thought I
> could probably reasonably attempt to grok qtHaskell at this point.
>
> My main question is: anyone recommended a good explanation of the foreign
> function or foreign pointer interface?
>
> My immediate question is that I was poking through the Qtc docs, and saw
> this:
>
>
> Documentation
>
> data Object a
>
> Constructors
>
> QObject !(ForeignPtr a)
>
> I am not sure how Haddock works. Is this telling me that an Object
> constructor takes one argument, which is of type QObject, where QObject is
> a type constructor that takes !(ForeignPtr a)? Or is this saying it takes
> two arguments, a QObject and a !(ForeignPtr a). That latter makes more
> sense I guess. What does the ! mean?
It tells you that the (Object a) datatype has a data-constructor called QObject
(I know
you already figured that out) which takes one argument of type (ForeignPtr a).
However, the constructor's argument type has a bang (!), which means that the
constructor
is strict in its argument.
For nonstrict constructors (data Ob a = Con a), you can happily create a value
Con _|_
which will be a nice and harmless citizen until you try to look at its
contents. For
example,
let x = Con undefined in x `seq` 3
returns 3, only
let x = Con undefined in
case x of
Con y -> y `seq` 3
will raise an exception.
If you make your constructor strict (data Thing a = SCon !a), it doesn't accept
a bottom,
the strict constructor evaluates its argument to weak head normal form, if it
encounters a
bottom, an exception is raised.
So,
Con _|_ /= _|_
but
SCon _|_ == _|_
>
> Thanks,
> Mike
------------------------------
Message: 7
Date: Mon, 7 Sep 2009 19:44:03 -0400
From: Andrew Wagner <[email protected]>
Subject: Re: [Haskell-beginners] idiomatic haskell question
To: Tom Doris <[email protected]>
Cc: [email protected]
Message-ID:
<[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
First of all, I highly recommend reading John Hughes' paper "Why Functional
Programming Matters" (http://www.cs.chalmers.se/~rjmh/Papers/whyfp.pdf) to
get a grasp of how to write alpha-beta and similar algorithms functionally.
Secondly, I've been playing around lately with representing tree traversals
as operations on a zipper. That is:
type TreeTraversal a = State (TreeLoc a)
This would allow you to cleanly write a traversal function which would
"return" a score, but also have, as its state, a focus on the node which it
has selected, from which you could easily get a path. See some of the top
results at http://www.google.com/search?q=haskell+zipper for a refresher on
zippers if needed. I hope to release a library around this code some day
soon.
On Mon, Sep 7, 2009 at 1:28 PM, Tom Doris <[email protected]> wrote:
> Hi all, I've recently started using Haskell and am looking for some
> feedback on code I've written; I sometimes feel that maybe I'm not doing
> things the best way possible that Haskell allows, and maybe missing out on
> obvious improvements in brevity or elegance. So here's a tic-tac-toe solver
> I wrote that does basic min-max search of the entire tree (not efficient
> algorithmically, but it's tictactoe so a blank board can be fully solved in
> a few seconds). Also, if people have suggestions on how to change the
> program to actually output the moves it would make, please let me know -
> right now it just responds with 1 for a win for X, 0 for a draw, and -1 for
> a win for O. And there are probably bugs!
> Thanks in advance
>
> import Data.List
> data Box = Blank | X | O deriving (Eq, Show)
> -- usage: call score with the board rows concatenated: score [Blank, Blank,
> Blank, Blank, Blank, Blank, Blank, Blank, Blank]
> -- or score [Blank, X, O, Blank, X, O, Blank, Blank, Blank]
> -- score is 1 if X wins, 0 for draw, -1 for lose
>
> score :: [Box] -> Int
> score g | haveline X g = 1
> | haveline O g = -1
> | gridfull g = 0
> | isxmove g = maximum (map score (makeallmoves X g))
> | otherwise = minimum (map score (makeallmoves O g))
>
> tolines :: [Box] -> [[Box]]
> tolines [a1, a2, a3, b1, b2, b3, c1, c2, c3] = [ [a1,a2,a3], [b1,b2,b3],
> [c1,c2,c3],
> [a1,b1,c1], [a2,b2,c2],
> [a3,b3,c3],
> [a1,b2,c3], [a3,b2,c1] ]
>
> haveline :: Box->[Box] -> Bool
> haveline b g = any ([b,b,b]==) (tolines g)
>
> gridfull :: [Box] -> Bool
> gridfull g = not $ any (Blank==) g
>
> isxmove :: [Box] -> Bool
> isxmove g = let movecount = sum $ map (\b -> if b==Blank then 0 else 1) g
> in mod movecount 2 == 0
>
> isomove = not . isxmove
>
> fl :: Box->[Box]->[Box]->[[Box]]
> fl b xs (Blank:ys) = [xs ++ b:ys]
> fl _ _ _ = []
>
> makeallmoves :: Box->[Box]-> [[Box]]
> makeallmoves b g = concat $ zipWith (fl b) (inits g) (tails g)
>
>
>
>
>
>
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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