Re: [Haskell-cafe] Haskell image libraries
On Sun, 2009-11-08 at 16:34 +0200, Max Rabkin wrote: To add image support to fdo-notify, I need an image type. Looking through Hackage, I didn't find any image library with the following features: * Load from a variety of formats (at least PNG and JPG, I'd say) * Efficient per-pixel access, or a way to dump the image into a ByteString as a bitmap (I need to serialise them into the protocol's bitmap format) Preferably, it should be possible to construct images programmatically too. What about the imlib bindings [1]? The only problem is, that imlib doesn't provide a functional image type (you'll end up processing the image in the IO monad), but it works quite well (I used it for my Piet interpreter, which required basic image processing tasks like a labelling algorithm). HTH - Stephan [1] http://hackage.haskell.org/package/Imlib -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Cabal packages - cabbages
Jon Fairbairn wrote: Conor McBride co...@strictlypositive.org writes: On 20 Sep 2009, at 23:11, Jason Dusek wrote: Some day, we're going to need a short, catchy name for Cabal packages. Let's call them cabbages. Not that this is a good reason to change your mind, but some sufficiently ancient Brits may remember a televisual Speaking of ancient Brits, the Finns used to call Britain cabbage-land, in case that alters anyone's opinion. Speaking of ambiguities: http://en.wikipedia.org/wiki/Cabbage_%28disambiguation%29 CABG is especially interesting :) //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Questions about haskell CPP macros
Matthew Elder wrote:
{-# LANGUAGE CPP #-}
main = putStrLn (__FILE__ ++ : ++ show __LINE__)
This outputs:
test.hs:2
Unfortunately, if your file is in a hierarchy of folders, this flat file
name doesn't give much context. Is there a macro to find out the current
module? IE if I had a module Foo.Bar.Car.MyModule, I would like to be
able to output something like this on error:
Foo.Bar.Car.MyModule:2
As mentioned by Claus, template-haskell offers a solution. But in some
cases, this is an overkill; consider using Control.Exception.assert, it
will provide module and line information without having to use CPP:
myHead :: [a] - a
myHead (x:_) = x
myHead []= assert False undefined
[...]
//Stephan
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Re: [Haskell-cafe] Questions about haskell CPP macros
Malcolm Wallace wrote:
{-# LANGUAGE CPP #-}
main = putStrLn (__FILE__ ++ : ++ show __LINE__)
This outputs:
test.hs:2
if I had a module Foo.Bar.Car.MyModule, I would like to be able to
output something like this on error:
Foo.Bar.Car.MyModule:2
It works for me. If you place that text in Try/Me.hs and call
ghc -E Try/Me.hs
you get
Try/Me.hs:2
If you just want to turn slashes into dots, and remove the suffix, that
is a simple exercise in Haskell itself
main = putStrLn (mangle __FILE__)
where mangle ('/':cs) = '.': mangle cs
mangle .
Careful, '/' might be '\\' on another OS, the file might end with .hsc
instead of .hs, the line numbers might not fit in the .hsc case...
--
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Re: [Haskell-cafe] Re: Adding an ignore function to Control.Monad
Johan Tibell wrote: [...] I also think void is clearer than ignore. So do I. Another point is, that it's familiar from other languages; a function void f(...) doesn't return anything but may have an effect on the environment. Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Code walking off the right edge of the screen
Henning Thielemann wrote: [...] http://haskell.org/haskellwiki/Case Maybe we (i. e. someone with a wiki account ;) ) should add Jeremy's proposal - using let and guards - to the page (under section 2.2, syntactic suger)? IMHO this is much clearer than case () of _. foo = let x | 1 1 = uh-oh | otherwise = all is well in x Regards, Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Code walking off the right edge of the screen
Deniz Dogan wrote: I (too) often find myself writing code such as this: if something then putStrLn howdy there! else if somethingElse then putStrLn howdy ho! else ... [...] So how do I make code like this prettier? If it's a function, you can use guards: foo :: ... foo something somethingElse | something - putStrLn howdy there! | somethingElse - putStrLn howdy ho! | otherwise - ... -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] curious about sum
Jochem Berndsen wrote: Keith Sheppard wrote: Is there any reason that sum isn't strict? I can't think of any case where that is a good thing. Prelude sum [0 .. 100] *** Exception: stack overflow It is useful if the (+) is nonstrict; although I cannot think of any useful mathematical structure where (+) would be nonstrict. What about some numeric representations? type MyNum = [()] instance Num MyNum where (+) = (++) Regards, Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Monad transformer responsibilities
Henning Thielemann wrote: [...] - So you have to declare them near the test cases and they're orphan instances The entire project doesn't issue a single warning when compiling with -Wall *except* two orphan instances when building the test cases... However, I had sometimes the case, where a type from another library was part of my tests and thus I needed its Arbitrary instance. I could have defined instances for the foreign types, but they would have been orphan and I risk that the library author decides to add the instances later. Hmm... maybe it is a good idea to aktivate the instance declaration with a cabal flag? I've already got: Flag Test Description: Build a binary running test cases Default: False and I could easily add something like if flag( Test ) CPP-Options: -D__TEST__ Build-Depends: QuickCheck = 2 3 and data MyType = ... #ifdef __TEST__ instance Arbitrary MyType where ... #endif A usage of cabal flags that strongly reminds me of Gentoo's useflags :) However, this will result in a total mess with more than one such flag... //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Monad transformer responsibilities
Hi, it's alomost the same problem when you're writing a library with optional quickcheck test cases: Where to put the Arbitrary instances? - You can't put them into quickcheck - You don't want to put them in the library (because of the quickcheck dependency) - So you have to declare them near the test cases and they're orphan instances The entire project doesn't issue a single warning when compiling with -Wall *except* two orphan instances when building the test cases... //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: heap-1.0.0
Hello haskell-cafe,
I'm pleased to announce a rewrite of the heap package, heap-1.0.0 [1].
It is not 100% compatible to the version 0.6.0, but provides major
improvements:
- The HeapPolicy type class hack used to distinguish between min- max-,
min-prio- and max-prio-heaps has been replaced by the HeapItem type
family (the type family provides functions to convert insertable
'items' to (priority, value) pairs and back. Thus a static min-heap
(HeapT) can be used as underlying implementation, but the package can
still provide MinHeap, MaxHeap, MinPrioHeap and MaxPrioHeap.
- A nice side effect of the above is, that ({Min,Max}PrioHeap p) now
is an instance of Functor
- Faster {from,to}{Asc,Desc}List conversions
- A binary with quickcheck test cases can now be built from cabal (with
a Test flag) (the old versions already had lots of test cases, but
cabal didn't know about them).
Regards,
Stephan
[1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/heap-1.0.0
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Re: [Haskell-cafe] Why is Bool no instance of Num and Bits?
Neil Mitchell wrote: [...] Which is a shame, having Bits on Bool seems entirely logical, having Num a superclass of Bits seems a little less clear. There are two default implementations in Bits bit i = 1 `shiftL` i x `testBit` i = (x .. bit i) /= 0 which rely on Num (and on the fact that 0 ~= 0..0 and 1 ~= 0..01, which doesn't have to be the case in all Num instances?). But is that worth having Num as superclass? When declaring in instance for Bits you have to implement at least 8 functions anyway so these two IMHO don't really make a difference, do they? //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Why is Bool no instance of Num and Bits?
Hi! When looking for an xor function, I found one in Data.Bits but couldn't use it for Bool, because Bool is no instance of Bits and of Num (which would be necessary, because it's class (Num b) = Bits b). My question is: Why not? We could declare instance Num Bool where (+) False = id (+) True = not (*) True True = True (*) _ _= False (-) = (+) negate = id abs = id signum = const True fromInteger = not . even which basically implements the field with 2 elements and instance Bits Bool where bitSize = const 1 isSigned = const False (..) = () (.|.) = (||) xor = (+) complement = not shift = const shiftL = const shiftR = const rotate = const rotateL = const rotateR = const bit = (==0) setBit _ 0 = True setBit b _ = b clearBit _ 0 = False clearBit b _ = b complementBit b 0 = not b complementBit b _ = b testBit b 0 = b testBit _ _ = False quite trivial... Why is this not part of base? Or am I missing something? //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why is Bool no instance of Num and Bits?
Deniz Dogan wrote: instance Num Bool where (+) False = id (+) True = not (*) True True = True (*) _ _= False Isn't XOR for booleans (/=)? Oh right. And (*) would be (): instance Num Bool where (+) = (/=) (*) = () -- ... //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Trouble with type signatures and type families
Hi, consider the following code: class Foo f where type Bar f :: * type Baz f :: * from :: Bar f - Baz f to :: Baz f - Bar f data Tree a b c = Empty | Tree b c (Tree a b c) (Tree a b c) --singleton :: (Foo f) = Bar f - Tree a (Bar f) (Baz f) singleton x = Tree x (from x) Empty Empty what type does 'singleton' have? ghci-6.10.2 says: :t singleton singleton :: forall f a. (Foo f) = Bar f - Tree a (Bar f) (Baz f) which is no surprise. But when I uncomment the type signature in the above code sample, loading it to ghci gives the following error: :r [1 of 1] Compiling Main ( T.hs, interpreted ) T.hs:14:22: Couldn't match expected type `Baz f1' against inferred type `Baz f' In the second argument of `Tree', namely `(from x)' In the expression: Tree x (from x) Empty Empty In the definition of `singleton': singleton x = Tree x (from x) Empty Empty T.hs:14:27: Couldn't match expected type `Bar f' against inferred type `Bar f1' In the first argument of `from', namely `x' In the second argument of `Tree', namely `(from x)' In the expression: Tree x (from x) Empty Empty Failed, modules loaded: none. I don't get it... what's wrong, I just copied the inferred type? //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Trouble with type signatures and type families
Gleb Alexeyev wrote: You may want to read the comments at http://hackage.haskell.org/trac/ghc/ticket/1897. Wow that's subtle... Thanks a lot! -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Monad transformer to consume a list
Henning Thielemann wrote: is there a monad transformer to consume an input list? I've got external events streaming into the monad that are consumed on demand and I'm not sure if there's something better than a StateT. I wondered that, too. I wondered whether there is something inverse to Writer, and Reader is appearently not the answer. Now I think, that State is indeed the way to go to consume a list. Even better is StateT List Maybe: next :: StateT [a] Maybe a next = StateT Data.List.HT.viewL -- see utility-ht package But a StateT provides the power to modify the list in other ways than reading the first element (modify (x:)). Maybe ParsecT is closer to what I'm looking for ;) -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Monad transformer to consume a list
My solution is this transformer:
newtype ConsumerT c m a
= ConsumerT { runConsumerT :: [c] - m (a, [c]) }
instance (Monad m) = Monad (ConsumerT c m) where
return x = ConsumerT $ \cs - return (x, cs)
m = f = ConsumerT $ \cs - do
~(x, cs') - runConsumerT m cs
runConsumerT (f x) cs'
fail msg = ConsumerT $ const (fail msg)
consume :: (Monad m) = ConsumerT c m (Maybe c)
consume = ConsumerT $ \css - case css of
[] - return (Nothing, [])
(c:cs) - return (Just c, cs)
consumeAll :: (Monad m) = ConsumerT c m [c]
consumeAll = ConsumerT $ \cs - return (cs, [])
--
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[Haskell-cafe] Monad transformer to consume a list
Hello, is there a monad transformer to consume an input list? I've got external events streaming into the monad that are consumed on demand and I'm not sure if there's something better than a StateT. //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Optional EOF in Parsec.
Kannan Goundan wrote: I'm writing a parser with Parsec. In the input language, elements of a sequence are separated by commas: [1, 2, 3] However, instead of a comma, you can also use an EOL: [1, 2 3] Anywhere else, EOL is considered ignorable whitespace. So it's not as simple as just making EOL a token and looking for (comma | eol). Hi Kannan, let's construct the parser top-down. On the top level, you have opening and closing characters, '[' and ']'. Parsec has a function for that: between (char '[') (char ']) And what's in between? A list of elements separated by something. Parsec provides a sepBy function for that: element `sepBy` separator which parses a list of elements separated by separator. What's your separator? Well it's either ',' or a new line and spaces before and after that: mySpaces (newline | char ',') mySpaces -- [1] Let's combine what we've got: myListOf :: (Parsec String () a) - Parsec String () [a] myListOf elem = between (char '[') (char ']') (elem `sepBy` (mySpaces (newline | char ',') mySpaces)) where mySpaces = many (oneOf ( \t)) And test it in ghci: *Main parseTest (myListOf anyChar) [a , b, d ,d\np] abddp Hope this helps! Stephan PS: The important thing is that there are a lot solutions for tricky situations (like yours) in Text.Parsec.Combinator (especially the sepBy and many families). Knowing them can save a lot of work :) [1] I don't use parsec's spaces function because it also accepts newline characters. I've implemented this functionality in a hand-written parser (basically a hack that keeps track of whether the last read token was preceded by an EOL, without making EOL itself a token). Does anybody have ideas about how to do this with Parsec? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Template Haskell messes up scoping?
Hi,
when I tried to reorganize some code to use the data-accessor and
data-accessor-template packages, i stumbled across a strange effect:
When using template haskell some things are out of scope that really
shouldn't be. Let me give an example:
== T.hs ==
{-# LANGUAGE TemplateHaskell #-}
data Foo = Foo
{ bar :: Bar
}
$( return [] )
data Bar = Bar
==
ghci T.hs
GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer ... linking ... done.
Loading package base ... linking ... done.
[1 of 1] Compiling Main ( T.hs, interpreted )
T.hs:4:13: Not in scope: type constructor or class `Bar'
Failed, modules loaded: none.
No matter what you do in $( ... ), the code doesn't compile. Even in the
simple case above, it doesn't work. What's happening here? Bug or
feature? And do you know a workaround?
//Stephan
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Re: [Haskell-cafe] Template Haskell messes up scoping?
Hi Martijn,
Martijn van Steenbergen wrote:
[...]
Apart from the specific problematic file you gave, I had some other
scoping issues when using TH to generate the accessors. I worked around
this by defining my data types in a separate module Types and calling
the TH functions in that module as the last lines. [...]
looks like your workaround also works in this case. This file (the
template instanciation was moved to the last line) compiles:
== T.hs ==
{-# LANGUAGE TemplateHaskell #-}
data Foo = Foo
{ bar :: Bar
}
data Bar = Bar
$( return [] )
==
It looks like the scope is interrupted just above $( ... ) - but I'd
like to know why and find a more beautiful way than just moving all th
calls to the bottom of the module file :)
Regards
Stephan
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[Haskell-cafe] View patterns and warnings about overlapping or non-exhaustive patterns
Hi,
I'm working on a data structure that uses Data.Sequence a lot, so views
are important and I tried to simplify my code using view patterns.
The problem is, that I keep getting warnings about both overlapping and
non-exhaustive pattern matches. A simple test case:
===T.hs===
{-# LANGUAGE ViewPatterns #-}
import Data.Sequence
test :: Seq a - Seq b - String
test (viewl - EmptyL) (viewl - EmptyL) = empty, empty
test (viewl - EmptyL) (viewl - _ : _) = empty, non-empty
test (viewl - _ : _) (viewl - EmptyL) = non-empty, empty
test _ _ = non-empty, non-empty
==
ghci -Wall T.hs
GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer ... linking ... done.
Loading package base ... linking ... done.
[1 of 1] Compiling Main ( T.hs, interpreted )
T.hs:6:0:
Warning: Pattern match(es) are overlapped
In the definition of `test':
test ((viewl - EmptyL)) ((viewl - EmptyL)) = ...
test ((viewl - EmptyL)) ((viewl - _ : _)) = ...
test ((viewl - _ : _)) ((viewl - EmptyL)) = ...
test _ _ = ...
T.hs:6:0:
Warning: Pattern match(es) are non-exhaustive
In the definition of `test': Patterns not matched:
Ok, modules loaded: Main.
*Main test empty (singleton 'a')
empty, non-empty
*Main test (singleton 'b') (singleton 'a')
non-empty, non-empty
*Main test (singleton 'b') empty
non-empty, empty
*Main test empty empty
empty, empty
There are warnings about non-exhaustive and overlapping pattern matches,
but the tests show that this isn't the case. So what's the problem? I
don't want to turn off or ignore warnings.
//Stephan
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Re: [Haskell-cafe] View patterns and warnings about overlapping or non-exhaustive patterns
Svein Ove Aas wrote: [...] For the time being, it will *work*, you just won't get useful warnings. Hopefully it's going to be fixed for 10.2. Hmm I don't find #2395 anywhere on http://hackage.haskell.org/trac/ghc/milestone/6.10.2 :( //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] question on types
Daryoush Mehrtash wrote: Is there a way to define a type with qualification on top of existing type (e.g. prime numbers)? Say for example I want to define a computation that takes a prime number and generates a string. Is there any way I can do that in Haskell? Haskell's type system is decidable, so you can't let the type system check arbitrary properties. It probably is possible in C++ by some template hack (C++ templates are Turing complete), but not in Haskell. But, as mentioned in the other responses, you can - use a representation that makes it impossible to use wrong values (- Ketil's n-th prime representation) - check values at runtime (- Luke's repsonse) //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] UDP
Andrew Coppin wrote: I'm trying to write a simple program that involves UDP. I was hoping something like this would work: [...] How about using bindSocket? At least that's the main difference between your code snippet and our (UDP-using) barracuda project :) main2 = do s - socket AF_INET Datagram defaultProtocol bindSocket s ... putStrLn Waiting... x - recv s 100 putStrLn x [...] //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haddock bug for strict unpacked fields?
Hi,
using haddock-2.4.1 and this file:
module Test where
data Test
= NonStrict Int
| Strict !Int
| UnpackedStrict {-# UNPACK #-} !Int
The generated documentation looks like this:
data Test
Constructors
NonStrict Int
Strict !Int
UnpackedStrict !!Int
Note the double '!' in the last constructor. This is not intended
behaviour, is it?
//Stephan
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Re: [Haskell-cafe] Stupid question #852: Strict monad
Hello Brian, Brian Hurt wrote: [...] So today's question is: why isn't there a Strict monad? Something like: data Strict a = X a instance Monad Strict where ( = ) (X m) f = let x = f m in x `seq` (X x) return a = a `seq` (X a) unless I am mistaken, this violates the first monad law (see Prelude documentation) return a = k == k a for k = const (return 3) and a = undefined, because return undefined = _ === _|_ but const (return 3) undefined === return 3 Generally speaking, the first monad law only holds for strict functions in your monad. [...] Happy new year, Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] followedBy parser in Parsec
Paul Keir wrote: Is there a way in Parsec to check what the next token is, and if it is what you're hoping for, leave it there. Maybe you're looking for 'lookAhead'? [...] //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: cabal install HaXml installs wrong version unless I specify the version number
Don Stewart wrote: [...] Note that packages that depend on the 'experimental' versions of things (in particular Haxml 1.19.* can't be packaged for Arch either, as we can only install one version of the haskell-haxml package). In this case we definetely need haxml-1.19. IIRC we even committed patches to the haxml repository, when we were developing Barracuda a year ago :) //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: cabal install HaXml installs wrong version unless I specify the version number
Thomas Hartman wrote: When I specify Build-Depends: base, parsec, HaXml = 1.19.4 in xml-parsec.cabal it does install correctly. I just fixed xml-parsec.cabal and uploaded it on hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xml-parsec-1.0.3 [...] //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Hackage Build Failures
Emil Axelsson wrote: [...] The error comes from using QuickCheck 2, which happens to also use the operator (). I can see two ways to solve the problem: (1) Add 2 after QuickCheck in the Wired.cabal file. (2) Add hiding (()) after import Test.QuickCheck in Data/Hardware/Internal.hs Emil, my suggestion is: Please use alternative (2), at least if there are no further problems with quickcheck 2! Otherwise, depending on quickcheck 2 just introduces unnecessary package incompatibilities. [...] //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Red-Blue Stack
apfelmus wrote: [..] Persistent data structures are harder to come up with than ephemeral ones, [...] Yes, in some cases it's quite hard to find a persistent solution for a data structure that is rather trivial compared to its ephemeral counterpart. My question is: Is there a case, where finding a persistent solution that performs equally well is *impossible* rather than just harder? I mean might there be a case where (forced) persistence (as we have in pure Haskell) is a definite disadvantage in terms of big-O notation? Do some problems even move from P to NP in a persistent setting? Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Line noise
Andrew Coppin wrote: [...] - Variable names such as x and f aren't fabulously helpful to lost programmers trying to find their way. I'm not a fan of cryptic variable names, either, and I try to use descriptive names wherever I can. But in Haskell... - ... you often have variables, which have a scope of far less than a line such as in map (\(x, (_, y)) - (x, y) ... (cleaning intermediate results from a list). - ... things often get very abstract, so that it just feels wrong matching on, say, (socket:sockets) instead of (x:xs). [...] //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Views
Johannes Waldmann wrote:
a) ... to use Maybe
b) ... to provide my own Data.Heap.View type
leave the choice up to the programmer,
and provide a generic interface,
accepting any MonadZero (*) instance.
cf. Data.Set.maxView
AFAIK there has been a vivid discussion about that. I think the crux of
the matter was that a monad is too general. Either there is a result or
there is not. That's precisely the intended use of a Maybe.
Besides, I just learned that Data.Map.{lookup,minView,maxView} and the
like have been modified to return a Maybe in the current GHC head
branch, see [1]. This suggests using Maybe in my case as well.
[...]
[1]
http://www.haskell.org/ghc/dist/current/docs/libraries/containers/Data-Map.html
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Re: [Haskell-cafe] Views
Johannes Waldmann wrote: I think the crux of the matter was that a monad is too general. Either there is a result or there is not. That's precisely the intended use of a Maybe. Indeed Monad m = is dangerous here because not every Monad has a reasonable definition of fail. But that seems to be a problem in the (current) definition of Monad, and its solution was MonadZero, no? I agree that the MonadZero class with a useful 'zero' :: m a would be the right abstraction for views. But MonadZero is not part of base, mtl or any other common package, or am I missing something? Changing this is beyond a simple heap package ;) -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Views
Hello! List-like data structures should IMHO provide safe versions of 'head' and 'tail' (with safe I mean 'not partial', i. e. functions that don't provoke an 'error' when called with an empty collection). As far as I know, this is usually called 'view' and and has a type signature like view :: SomeDataStructure a - View a with data View = Empty | Cons a (SomeDataStructure a) A good example for this is Data.Sequence. My question is: Why is this not expressed in terms of Maybe? view :: SomeDataStructure a - Maybe (a, SomeDataStructure a) This would be easier to use, as there's no need for a new View type and because Maybe already provides instance declarations for a lot of useful classes (Functor, Monad, etc.) and handy helper functions (e. g. 'maybe'). Then you could, for instance, say: head xs = maybe undefined fst (view xs) tail xs = maybe undefined snd (view xs) You can of course argue that you want viewl and viewr to have different types in the case of Data.Sequence, but this is not the case for other, rather one-ended, data types, is it? Long story short, my problem is the following: I want to provide a 'view' function for Data.Heap in my heap [1] package and I don't know whether... a) ... to use Maybe b) ... to provide my own Data.Heap.View type c) ... a Data.View package with a View type should be included in the containers- or even base-package. This would prevent lots of small projects from creating totally equivalent View types. Maybe there even exists a Data.View package that I didn't find? Regards, Stephan [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/heap-0.3.1 -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] language proposal: ad-hoc overloading
Miguel Mitrofanov wrote: Suppose you have different thing all named insertWith. You've got one somewhere in your program; how do YOU know when looking at the code after a month or so, which one is this? We already have that situation when classes are involved. If you replace specialised functions by abstractions provided classes, for instance mempty instead of Data.Structure.empty fmap instead of Data.Structure.map folds from Data.Foldable instead of a specialised module There certainly are more examples, but these are the most common. IMHO this doesn't make code much harder to read. mempty gives us some empty data structre, fmap applies a function to all its elements and folds do the same. It doesn't matter if we're talking about lists, sets or something else. And it has the huge advantage that you can replace a data structure by another (Maybe by [], [] by Set, ...) simply by changing a type signature and not the code. Certainly, given a smart IDE you can ask it; but I think that code should be clear just when you look at it, without any action. I think that - at least in the examples listed above - the code remains very clear. [...] Regards, Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Pure hashtable library
Bulat Ziganshin wrote: solving one more task that uses English dictionary, i've thought: why we don't yet have pure hashtable library? There is imperative hashtables, [...] how should it look: * hashtable is represented as an array of assoc lists: Array Int [(a,b)] Don't immutable arrays get rather inefficient when modified? [...] Just a tought: You might want to have a look at the bloom filter implementation. On one hand, it is an alternative for your dictionary and on the other and, its implementation uses hash functions and arrays as well. IIRC it does that in a state monad that keeps the array mutable and finally freezes it before usage, which might be a good idea for pure hash table as well. //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: [Haskell] ANN: random-access-list-0.1
Isaac Dupree wrote: [...] Well Chris Okasaki called them Skew Binary Random-Access Lists, which is even longer :) :) hmm.. IndexableList? (just a thought, not sure whether I like it any better) RAList? IList? - (will I be sued by a large computer company for that?) [...] Yes, I wasn't happy with that one either. The view-concept of Data.Sequence is a good idea. yeah, it's a good idea, although I'm not sure how much I like the particular syntax of how it's done in Data.Sequence (the view-types' constructor names, mostly) I now have data View a = Empty | Cons a (RandomAccessList a) and view :: RandomAccessList a - a additionally, I renamed extractHead to uncons (which is OK, because I also have cons) but still left head and tail with the typical list-like behaviour (causing an error on empty lists). [Monad vs. Maybe] That's quite convincing, most of all that fail has rather strange definitions for many Monads (because it originally does not belong to monads, does it?). [...] The size function is in O(1) because I cache it, otherwise it would be size (RandomAccessList xs) = sum (map fst xs) which is O(log n). I consider the caching useful, as most applications will check 0 = i size quite often. sounds good [...] If two lists have exactly the same size, all the complete binary trees holding the data have the same size as well. This can be zipped directly and is a bit (~5% in my tests) faster. okay, that sounds like a fair optimization, since zipping same-size lists is a nice thing to do anyway. But the asymptotic speed ideally should still be O(min(m,n)), if possible? Well... I guess that's possible converting the shorter one into a list and using fold for zipping. I'll have a close look at this! -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: [Haskell] ANN: random-access-list-0.1
Isaac Dupree wrote:
[...]
Great to see it, it deserved implementing, IIRC! I don't remember
enough about it.. (and don't have Okasaki anywhere handy). Can it be
lazy or infinitely long?
No, it has to be finite as it's actually a list of complete binary trees
whose size depend on the skew binary representation of the list's size.
I'll document this.
[...]
Is RandomAccessList the best name for something that's not O(1),
just O(log n)? Or just that RandomAccessList is just much longer than
[]?
Well Chris Okasaki called them Skew Binary Random-Access Lists, which
is even longer :)
don't use those unorthodox infix function names.. `cons` is hardly
worse than .:. , `append` or `mappend` than .+. , and .!. than, hmm.. .
Export a ++ and ! (!! ?) if you're really dedicated. But I'd prefer an
`at` that's the same partial indexing operation, rather than the name
.!. (I think this at was a new name being put somewhere else? partly
because ! is trying to be gradually used only to refer to strictness?)
Good point!
extractHead is an ugly name for a nevertheless standardish-meaning
function... what is it usually called? uncons? headTail? (Data.Sequence,
which is meant to be left-right symmetric, calls it viewr... except
your version doesn't have the Maybe, it's partial instead, fails on
empty lists)
Yes, I wasn't happy with that one either. The view-concept of
Data.Sequence is a good idea.
For index, don't use Monad, use Maybe (I think that's what the
recent [EMAIL PROTECTED] discussion concluded, in the context of
switching Data.Map back to Maybe).
I was just copying the idea from Data.Map and it's usually a good thing
to have functions as general as possible, or why is it not?
Also, Data.List has genericLength etc, to
At the moment, I'm using the Int type for size and indexing only for one
reason: I haven't found a proper way to generalize it. I'd really like
to use the Ix class, but it doesn't provide enough functionality, it
only works on fixed-size intervals (i. e. for arrays, which don't change
their size, but a list does). Maybe someone has an idea of how to
realize lists with a variable starting index and size?
support. Isn't index (like Data.List.genericIndex) supposed to be
a name for a partial operation, not one that returns a Maybe? Shouldn't
size be named length (or exported as both names, since e.g.
Data.Map.size, .List.length) (why is it O(1) not O(log n)? Is it
possible for these RandomAccessLists to be longer than maxBound::Int?)?
The size function is in O(1) because I cache it, otherwise it would be
size (RandomAccessList xs) = sum (map fst xs)
which is O(log n). I consider the caching useful, as most applications
will check 0 = i size quite often.
for e.g. toList, is the O(n) cost spread over traversing/demanding
the items of the generated list, or all up-front, or somewhere in between?
Why is zip slow with unbalanced lists? Obviously, it could be
implemented O(min(m,n)*(log m + log n)) just indexing each one, which
would be faster for really unbalanced-size lists... Obviously, I don't
If two lists have exactly the same size, all the complete binary trees
holding the data have the same size as well. This can be zipped directly
and is a bit (~5% in my tests) faster.
understand the implementation. BTW, looking at the file,
data RandomAccessList a
= RandomAccessList {-# UNPACK #-} !Int ![(Int, CBTree a)]
Marking a list strict like that doesn't have much effect because it
only makes the first (:) or [] strict. Did you mean for an
element-strict or spine-strict(which would necessarily be non-infinite)
list?
Oh, you're right, I just meant to mark the Int strict. It obviously was
too late yesterday!
Thanks for this feedback!
//Stephan
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Re: [Haskell-cafe] ANN: random-access-list-0.1
Chris Smith wrote: Chaddaï Fouché wrote: Given that this structure isn't lazy enough, I really don't see a problem with using Int (any random access list with a size that needs an Integer would blow the memory anyway...). Bad way to think about things. The implications of using Int as the result type of a function extend far beyond just storing the result type. They also include doing other computations that depend on the result type, and with enough type inference, the broken Int type propogates throughout the program. I'd like not to be restricted to Int, but what's the proper way to do so? Just adding genericFun = fromInteger . toInteger . fun functions is just as bad as using Ints directly. What I need is something like a more general Ix class that is not limited to a fixed interval: class Ix2 i where -- convert starting index and given index to an Int for internal -- representation toIndex :: i - i - Int -- given an internal Int index and a starting index, return the -- representing index fromIndex :: Int - i - i -- translate a starting index and a number of elements into a -- size size :: i - Int - i This is meant to work with a starting-index and a given index, so that a list does not have to start at index 0. Is there something like this? Or is it somehow possible to use the existing Ix class to do that? //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] question about STM and IO
Hello, John Lato wrote: I was recently looking at the STM library, and I have a question about the function unsafeIOToSTM. Can anyone explain to me what is unsafe about it, and what sort of use would be considered safe? it's unsafe to perform IO inside of a transaction as it can't be undone, when rolling it back. I guess, unsafeIOToSTM has been designed in order to allow us to inject debugging output into a transaction, but you really shouldn't use it to perform real IO (like writing files, etc.). HTH - Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: heap-0.2
A flexible heap implementation supporting min-, max- and custom-ordered heaps. New features since version 0.1: - Foldable and Read instance - filter, partition - subrange functions: take, drop, splitAt, takeWhile, span, break http://hackage.haskell.org/cgi-bin/hackage-scripts/package/heap-0.2.1 //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Data.Ord and Heaps (Was: Why functional programming matters)
Hi,
I'm sorry it took me so long to respond!
[EMAIL PROTECTED] wrote:
[newtype Ord a = Reverse a = Reverse { unReverse :: a }]
This solution should be used for all collections depending on Ord
instances, including Data.Map, Data.Set and others. As long as I only
include it in my tiny heap package, it is as 'non-standard' as my
approach, isn't it?
Yes. I mean non-standard in the software-reuse sense, i.e. Ord is for
user-defined orderings and should be the only such mechanism in order to
enable reuse. In fact, Data.Heap clearly shows that Data.Ord is
currently missing functionality.
Ah, now I see. The entire ordering policy mechanism - no matter how it
is going to be solved - belongs into Data.Ord and not in Data.Heap. As
soon as Data.Ord provides a solution, I'll use it in Data.Heap.
[...]
Note that the Heap class contains only three primitive operations
(empty, insert, viewHead), all the others have default implementations
in terms of those three. There is even an underappreciated unfold among
them :)
toAscList = unfoldr viewHead
The structure becomes especially clear by noting that any Heap is
defined by just two primitives
inject :: Ord a = Maybe (a, Heap a) - Heap a
view :: Ord a = Heap a - Maybe (a, Heap a)
We have inject = maybe empty (uncurry insert) . This is just like
lists, except that view . inject ≠ id since view returns the
smallest element.
I stumbled over the similarity of heaps and lists when implementing
take, takeWhile, span, break, etc. (btw, they are included in heap-0.2
which I uploaded yesterday); so a heap is really nothing but a packed
representation of a sorted list :)
However, just that we managed to reduce the number of primitive
operations doesn't mean that the policy approach isn't preferable. It
needs 0 primitive operations, after all. But as foreshadowed in my
reply, it's possible to do policies within Ord. Don't stop thinking
about your good idea just because you can start coding :)
Here's one way to do it:
[...]
In conclusion: the ordering policy stuff should not be part of
Data.Heap, this is a job for Data.Ord.
As mentioned above: This sounds really useful. How about you propose
this to the base-package maintainers? :)
What, me? :D
Where? :)
Regards, Stephan
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Re: [Haskell-cafe] NDP
Roman Leshchinskiy wrote: [...] Yes, me :-) Sorry for the late reply, it's been a long weekend here in Australia. Wow, Australia :) [...] I suspect that cd examples; make doesn't quite work at the moment because some of the examples are broken. I'll try to fix that soon. But cd examples/dotp; make should work. Hmm I must have missed that the ndp package didn't quite compile. Right now, I'm darcs pulling everything (ghc, libraries, ndp) and rebuilding it... ... and ghc failed. Looks like I have to wait for some patches. (.text+0x8d5): undefined reference to `__stginit_parallelzm1zi0zi0zi0_ControlziParallelziStrategies_' This is strange, I've never seen this. Can you please send me the exact commands you used to build ghc and package ndp and the complete log from making dotp? As far as I can remember: # in the ghc directory: darcs pull -a ./darcs-all pull -a sh boot ./configure make -j5 cd libraries darcs get --partial http://url/of/ndp/package/ make make.library.ndp I'm currently stuck at 'make -j5'. As soon as it works, I'll give you precise feedback. Roman Thank you! //Stephan PS: Is 'make clean' in the ghc directory enough for a complete rebuild? -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] NDP
Roman Leshchinskiy wrote: [...] You should make clean in ndp/examples. Sorry this doesn't happen automatically, the whole setup is a bit of a mess at the moment. Now it works, thanks a lot :) Sorry for the German make output, but I'm no admin on this machine No worries, I actually speak German :-) :D Roman //Stephan PS: ndp is a great technology, I can't wait to see it going stable :) -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: [Haskell] Why functional programming matters
Don Stewart wrote: stephan.friedrichs: [...] We [1] implemented an ad-hoc chat system in Haskell in the SEP [2] at the TU-Braunschweig. Wow! Looks like lots of great code in there, http://sep07.mroot.net/documentation/barracuda/ Text.ParserCombinators.Parsec.XML Codec.Encryption.PKCS1 Network.GnuTLS Data.Heap Will we see this packaged for hackage.haskell.org soon? Some of those modules look very reusable. I just uploaded a generalised heap (min-, max- and custom-heaps) implementation: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/heap-0.1 Feedback would be appreciated :) //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Crash in Data.ByteString.Lazy.hPut
Brandon S. Allbery KF8NH wrote: On Jan 28, 2008, at 17:33 , Jamie Love wrote: Shouldn't haskell pick up that there is no 'mod' for Word8? I mean, shouldn't I get a nicer error message? Hm? mod works fine for Word8, unless you specify a multiple of the type's bound. I think it's still hard for compilers to catch that for you Finding out if a variable will have a value of 0 is undecidable at compile time, isn't it? //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] NDP
Hi all, is someone familiar with compiling ndp (nested data parallel Haskell), Speed with less convenience-version? I followed the guide at http://www.haskell.org/haskellwiki/Data_Parallel_Haskell/PackageNDP but executing make in the examples directory issues the following error: (.text+0x8d5): undefined reference to `__stginit_parallelzm1zi0zi0zi0_ControlziParallelziStrategies_' manually compiling the dotp example on the link mentioned above doesn't work either: [...] (.data+0x5c): undefined reference to `ndp_DataziArrayziParallelziUnliftedziFlatziUArr_zdf14_closure' DotP.o: In function `sz3_srt': (.data+0x88): undefined reference to `ndp_DataziArrayziParallelziUnliftedziFlatziBasics_toU_closure' DotP.o: In function `sz3_srt': (.data+0x8c): undefined reference to `ndp_DataziArrayziParallelziUnliftedziFlatziUArr_zdf14_closure' /home/sfriedrichs/ghc/rts/libHSrts.a(Main.o): In function `real_main': Main.c:(.text+0x12): undefined reference to `__stginit_ZCMain' Main.c:(.text+0x2c): undefined reference to `ZCMain_main_closure' Does someone know, what's wrong? I'm using ghc-6.9.20080124 as source base (which compiled and works just fine). //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
