[Haskell-cafe] Re: (a - [b]) vs. [a - b]
Chad Scherrer wrote: Unfortunately, I was trying to give a simplification of the real problem, where the monad is STM instead of []. Based on apfelmus's observation of why they can't be isomorphic, I'm guessing I'm out of luck. http://www.haskell.org/pipermail/haskell-cafe/2006-December/020041.html So in reality, I'm trying to construct something like f :: (a - STM b) - STM (a - b) Indeed, such an f most likely does not exist. What is the task you tried to solve with the help of f? I guess that either there is a way without or it just cannot be solved for mathematical reasons. Regards, apfelmus ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Suggestions for a hReadUntilStr implementation
On 2/3/07, Matt Revelle [EMAIL PROTECTED] wrote: hReadUntilStr :: (Num a) = Handle - String - a - IO (String, Bool) Is this the wrong way to think about the problem? If so, how should it be handled? If not, any ideas on the implementation? Sounds like this would grow into a full-fledged expect-type program, in which case http://www.informatik.uni-bremen.de/uniform/wb/ is probably worth a look. martin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Alternate instance Show (Maybe a)?
On Feb 2, 2007, at 21:10 , Sergey Zaharchenko wrote:
Hello list,
Suppose I want show Nothing to return , and show (Just foo) return
show foo. I don't seem to be able to. Looks like I either have to use
some other function name, like `mShow', or have to import Prelude
hiding
Maybe, reimplement Maybe, write all the other useful instances
(Functor,
Monad) for it, etc. Not particularly hard, but looks ugly. Isn't
there a
better solution? I recall some discussion about this, but can't
find it
in the archives...
With GHC you can at least avoid rewriting all the instances: make a
newtype, use newtype deriving to get all the instances except Show,
and write your own Show instance.
{-# OPTIONS_GHC -fglasgow-exts #-}
newtype MyMaybe a = MyMaybe (Maybe a)
deriving (Eq,Ord,Monad,Functor)
instance Show a = Show (MyMaybe a) where
showsPrec _ (MyMaybe Nothing) = id
showsPrec n (MyMaybe (Just x)) = showsPrec n x
/Björn___
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Re: [Haskell-cafe] Re: (a - [b]) vs. [a - b]
On Sat, Feb 03, 2007 at 10:13:17AM +0100, [EMAIL PROTECTED] wrote: Chad Scherrer wrote: So in reality, I'm trying to construct something like f :: (a - STM b) - STM (a - b) Indeed, such an f most likely does not exist. Yes, consider: f readTVar :: STM (TVar c - c) That would be pretty dangerous. Best regards Tomasz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How did you stumble on Haskell?
On Jan 29, 2007, at 03:01 , Alexy Khrabrov wrote: How do people stumble on Haskell? Well, I didn't really stumble on it. I was at the 1987 meeting when we decided to define Haskell. But I stumbled on functional programming in the first place. I had to learn it because it was part of a course in denotational semantics. The language was SASL. And then I read David Turners paper on combinators, and I was hooked. -- Lennart ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How did you stumble on Haskell?
I'll go for the shortest story... I stumbled upon Simon's Composing Financial Contracts paper, Simon was gracious enough to spend a fair bit of time on the phone with me. The rest is history :-). Joel -- http://wagerlabs.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: How did you stumble on Haskell?
Lennart Augustsson [EMAIL PROTECTED] writes: On Jan 29, 2007, at 03:01 , Alexy Khrabrov wrote: How do people stumble on Haskell? Well, I didn't really stumble on it. I was at the 1987 meeting when we decided to define Haskell. But I stumbled on functional programming in the first place. I had to learn it because it was part of a course in denotational semantics. OK, if we old lags are going to give our excuses... I was a member of an undergraduate society in Cambridge called the Processor Group. I went along to a talk that Arthur Norman gave to them (must have been 1980±1?) in which he described (S, K, I) combinators and his plans for the SKI Machine (SKIM). The fact that S and K on their own gave a complete computational basis was the most exciting piece of computer science I'd encountered at that point and I just had to follow it up. So some years later I ended up at that same 1987 meeting. -- Jón Fairbairn [EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How did you stumble on Haskell?
In about 93 or 94 a colleague had talked to me about this wierd language called Haskell. At the time I hadn't listened because I was sure that Eiffel was the future. Besides, he had showed me a GUI demo: a calculator that took about half a second to register a button click. So I concluded that it wasn't practical. Fast forward to about 2001. I was in a job where I almost never got to do any programming. It had become painfully obvious that Eiffel wasn't going anywhere. I could always learn Java, but after Eiffel downgrading to Java felt like a sell-out: I wasn't going to do it. But I did want to learn a new language, and I'd read Eric Raymond's piece about being a hacker, where he said to learn Lisp for the side effects. I sort-of knew Lisp anyway, having done some Emacs Lisp hacking. But I felt I didn't really get it about FP. There seemed to be a lot of buzz about Haskell, so I took the plunge and started learning. Paul. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: How did you stumble on Haskell?
Paul Johnson [EMAIL PROTECTED] writes: I'd read Eric Raymond's piece about being a hacker, where he said to learn Lisp for the side effects. Much better to learn Haskell for the side effects! ;-) -- Jón Fairbairn [EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How did you stumble on Haskell?
Paul == Paul Johnson [EMAIL PROTECTED] writes: Paul because I was sure that Eiffel was the future. You were right! Paul It had become painfully Paul obvious that Eiffel wasn't going anywhere. Hm. Why do I make a living at it then? And why is there now an ECMA standard for it? Paul learn Java, but after Eiffel downgrading to Java felt like a Paul sell-out: That's true. Anyway, my story about how I stumbled across Haskell: I was visiting Glasgow for the Scottish Go championships, and was talking to John O'Donnell in the bar about what functional programming was all about. I mentioned that I knew Scheme, and he said he much preferred Haskell. So I tried to get him to describe the language to me, but he seemed more interested in playing Go. So I just had to learn it when i got home again, to find out about it. -- Colin Adams Preston Lancashire ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Proposal for allowing more use of layout to avoid parentheses and commas
Hi, Following a recent thread on the Haskell' mailing list about the nusiance of having to deal with commas in tuples (when cutting and pasting things to re-order the elements there's always a pesky comma left over in the wrong place), I've written up a proposal for a very simple syntax tweak that would allow you to use the layout rule for function arguments, tuple/list/record contents etc for some future version of Haskell at http://www.haskell.org/haskellwiki/Accessible_layout_proposal This post is not intended to spark a lot of discussion just to point out the existence of the page for anyone interested. I've also added a link to all the new proposals from http://www.haskell.org/haskellwiki/Future . (If I don't reply to any follow up posts to this thread it's not because I'm ignoring them. It will just be because I have to try to get down to actually writing more of my program in the next few weeks, and I find thinking up ideas and reading posts, books, cooking, shopping, watching dvds etc, is infinitely more diverting than the painstakingly hard work of actual coding (though of course it's great in the rare occasions when things fall into place) ... ;-)) Brian. -- http://www.metamilk.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Alternate instance Show (Maybe a)?
Hi Sergey, You wrote: Suppose I want show Nothing to return , and show (Just foo) return show foo. I don't seem to be able to. Looks like I either have to use some other function name, like `mShow' That is correct. Show instances are supposed to follow the convention that show x is a Haskell expression that recreates x. In other words, Show is mainly used for debugging, for simple serialization, and for interactive use in a Haskell shell like ghci or hugs. If you need to create strings from a datatype for some other reason, use a different function name. If you need to do it for several datatypes, create your own class. Of course, Show does turn out to be more generally useful for numeric types. Hope this helps. Regards, Yitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Space Leak Help
I have re-written SHA1 so that is more idiomatically haskell and it is easy to see how it implements the specification. The only problem is I now have a space leak. I can see where the leak is but I'm less sure what to do about getting rid of it. Here's the offending function: pad :: [Word8] - [Word8] pad xs = xs ++ [0x80] ++ ps ++ lb where l = length xs pl = (64-(l+9)) `mod` 64 ps = replicate pl 0x00 lb = i2osp 8 (8*l) I've thought about zipping the xs with [1..] which will give me a length as I go. Is this the right way to go are there better techniques for dealing with this? I've attached the full source below. Dominic. module Main(main) where import Data.Char import Data.Bits import Data.List import Data.Word import System import Codec.Utils type Rotation = Int rotL :: Rotation - Word32 - Word32 rotL s a = shiftL a s .|. shiftL a (s-32) instance Num [Word32] where a + b = zipWith (+) a b f n x y z | (0 = n) (n = 19) = (x .. y) .|. ((complement x) .. z) | (20 = n) (n = 39) = x `xor` y `xor` z | (40 = n) (n = 59) = (x .. y) .|. (x .. z) .|. (y .. z) | (60 = n) (n = 79) = x `xor` y `xor` z | otherwise = error invalid index for f k n | (0 = n) (n = 19) = 0x5a827999 | (20 = n) (n = 39) = 0x6ed9eba1 | (40 = n) (n = 59) = 0x8f1bbcdc | (60 = n) (n = 79) = 0xca62c1d6 | otherwise = error invalid index for k -- Word120 - Word512 - Word120 oneBlock ss xs = (as!!80):(bs!!80):(cs!!80):(ds!!80):(es!!80):[] where ws = xs ++ map (rotL 1) (zipWith4 xxxor wm3s wm8s wm14s wm16s) where xxxor a b c d = a `xor` b `xor` c `xor` d wm3s = drop (16-3) ws wm8s = drop (16-8) ws wm14s = drop (16-14) ws wm16s = drop (16-16) ws as = (ss!!0):ts bs = (ss!!1):as cs = (ss!!2):(map (rotL 30) bs) ds = (ss!!3):cs es = (ss!!4):ds ts = (map (rotL 5) as) + (zipWith4 f [0..] bs cs ds) + es + (map k [0..]) + ws ss :: [Word32] ss = [0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476, 0xc3d2e1f0] pad :: [Word8] - [Word8] pad xs = xs ++ [0x80] ++ ps ++ lb where l = length xs pl = (64-(l+9)) `mod` 64 ps = replicate pl 0x00 lb = i2osp 8 (8*l) blockWord8sIn512 :: [Word8] - [[Word8]] blockWord8sIn512 = unfoldr g where g [] = Nothing g xs = Just (splitAt 64 xs) getWord32s :: [Word8] - [Word32] getWord32s s = map f [0..15] where f i = foldl (+) 0 $ map (\n - toEnum (fromEnum (s!!(i*4+n))) `shiftL` (fromIntegral (8 * (3-n [0..3] blockWord32sIn512 :: [Word8] - [[Word32]] blockWord32sIn512 = (map getWord32s) . blockWord8sIn512 . pad -- Word120 - Word512 - Word120 hashOnce ss a = ss + oneBlock ss a hash = foldl' hashOnce ss . blockWord32sIn512 convert :: String - [Word8] convert = map (fromIntegral . ord) short :: [Word8] short = convert abc message :: [Word8] message = convert abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq performance n = (convert . take n . repeat) 'a' test n = mapM_ (putStrLn . show . hash) [short, message, performance n] main = do progName - getProgName args - getArgs if length args /= 1 then putStrLn (Usage: ++ progName ++ testSize) else test (read (args!!0)) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Space Leak Help
I have re-written SHA1 so that is more idiomatically haskell and it is easy
to
see how it implements the specification. The only problem is I now have a
space leak. I can see where the leak is but I'm less sure what to do about
getting rid of it.
Here's the offending function:
pad :: [Word8] - [Word8]
pad xs =
xs ++ [0x80] ++ ps ++ lb
where
l = length xs
pl = (64-(l+9)) `mod` 64
ps = replicate pl 0x00
lb = i2osp 8 (8*l)
I would try something along the following lines (untested):
\begin{spec}
catWithLen xs f = xs ++ f (length xs)
\end{spec}
\begin{code}
catWithLen :: [a] - (Int - [a]) - [a]
catWithLen xs f = h 0 xs
where
h k [] = f k
h k (x : xs) = case succ k of-- forcing evaluation
k' - x : h k' xs
\end{code}
\begin{code}
pad :: [Word8] - [Word8]
pad xs = catWithLen xs f
where
f l = 0x80 : ps lb
where
-- we know that |l = length xs|
pl = (64-(l+9)) `mod` 64
ps = funPow pl (0x00 :)
lb = i2osp 8 (8*l)
\end{code}
If you are lucky, then the replicate and the (++lb) in the original code
might be fused by the compiler as an instance of foldr-build
or something related --- check the optimised core code.
In my variant I changed this to rely on efficient function powering
instead:
\begin{spec}
funPow k f = foldr (.) id $ replicate k f
\end{spec}
\begin{code}
funPow :: Int - (a - a) - (a - a)
funPow n f = case compare n 0 of
LT - error (funPow: negative argument: ++ show n)
EQ - id
GT - pow n f
where
pow m g = if m 1
then let (m',r) = divMod m 2
g' = g . g
in if r == 0
then pow m' g'
else pow m' g' . g
else g
\end{code}
(You will probably also consider using Data.Bits
for (`mod` 64), (8*), and (`divMod` 2).
)
Wolfram
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Re: [Haskell-cafe] Space Leak Help
hi Dominic Explicit recursion works just fine for me and keeps things simple: pad :: [Word8] - [Word8] pad xs = pad' xs 0 pad' (x:xs) l = x : pad' xs (succ l) pad' [] l = [0x80] ++ ps ++ lb where pl = (64-(l+9)) `mod` 64 ps = replicate pl 0x00 lb = i2osp 8 (8*l) at the cost of (very slightly) hiding data flow. Seems exactly what you were trying to avoid? Cheers pepe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Suggestions for a hReadUntilStr implementation
Hi Matt, hReadUntilStr - that is, a function that takes a Handle as an input source, a String to match, and a Num a as the number of seconds to wait before returning a (String, Bool) where the String is all the text read from the Handle until either matching or timing out and the Bool is true if the input String was matched This might work for you: http://hpaste.org/289. It throws an IO exception if hWaitForChar times out, and makes use of lazy evaluation to schedule all the IO upfront so that grabbing the string prefix can be done in pure code. Thanks, Greg ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] The usage of runghc ?
I tried to install haskell-fastcgi ( http://www.cs.chalmers.se/~bringert/darcs/haskell-fastcgi/ ). runghc Setup.hs configure --prefix=$HOME/extra runghc -I$HOME/extra/include Setup.hs build Preprocessing library fastcgi-2006.10.9... FastCGI.hsc:50:21: error: fcgiapp.h: No such file or directory compiling Network/FastCGI_hsc_make.c failed command was: ghc -c Network/FastCGI_hsc_make.c -o Network/FastCGI_hsc_make.o Setup.hs: got error code while preprocessing: Network.FastCGI runghc --help runghc: syntax: runghc [-f GHCPATH] [GHC-ARGS] FILE ARG... ? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How did you stumble on Haskell?
Lennart, Now you've made me curious. Which paper is this? Is it available for download anywhere? Mike Lennart Augustsson wrote: On Jan 29, 2007, at 03:01 , Alexy Khrabrov wrote: How do people stumble on Haskell? Well, I didn't really stumble on it. I was at the 1987 meeting when we decided to define Haskell. But I stumbled on functional programming in the first place. I had to learn it because it was part of a course in denotational semantics. The language was SASL. And then I read David Turners paper on combinators, and I was hooked. -- Lennart ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How did you stumble on Haskell?
A new implementation technique for applicative languages, David A. Turner, Software — Practice and Experience, 9:31–49, 1979. I'm not sure if it's available online. -- Lennart On Feb 4, 2007, at 01:14 , Michael Vanier wrote: Lennart, Now you've made me curious. Which paper is this? Is it available for download anywhere? Mike Lennart Augustsson wrote: On Jan 29, 2007, at 03:01 , Alexy Khrabrov wrote: How do people stumble on Haskell? Well, I didn't really stumble on it. I was at the 1987 meeting when we decided to define Haskell. But I stumbled on functional programming in the first place. I had to learn it because it was part of a course in denotational semantics. The language was SASL. And then I read David Turners paper on combinators, and I was hooked. -- Lennart ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] The usage of runghc ?
On 2/4/07, keepbal [EMAIL PROTECTED] wrote: I tried to install haskell-fastcgi ( http://www.cs.chalmers.se/~bringert/darcs/haskell-fastcgi/ ). runghc Setup.hs configure --prefix=$HOME/extra runghc -I$HOME/extra/include Setup.hs build Preprocessing library fastcgi-2006.10.9... FastCGI.hsc:50:21: error: fcgiapp.h: No such file or directory compiling Network/FastCGI_hsc_make.c failed command was: ghc -c Network/FastCGI_hsc_make.c -o Network/FastCGI_hsc_make.o Setup.hs: got error code while preprocessing: Network.FastCGI You probably haven't installed fastcgi yet. See http://www.fastcgi.com/ -- Cheers, Lemmih ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Suggestions for a hReadUntilStr implementation
Thanks for the responses. Greg, your implementation looks useful but it's a little different than what I was thinking (my apologies, I wasn't very clear). In the implementation you posted, the timeout parameter is used to limit the amount of time spent waiting to read an individual character - I was hoping to use the timeout as an initial value for a timer that should start running when hReadUntilStr is evaluated and the function should finish evaluating when either the timer has run out or when the string match has been found. Martin, thanks for the link. Cheers, Matt On 2/3/07, Greg Fitzgerald [EMAIL PROTECTED] wrote: Hi Matt, hReadUntilStr - that is, a function that takes a Handle as an input source, a String to match, and a Num a as the number of seconds to wait before returning a (String, Bool) where the String is all the text read from the Handle until either matching or timing out and the Bool is true if the input String was matched This might work for you: http://hpaste.org/289 . It throws an IO exception if hWaitForChar times out, and makes use of lazy evaluation to schedule all the IO upfront so that grabbing the string prefix can be done in pure code. Thanks, Greg ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Alternate instance Show (Maybe a)?
Hello Yitzchak! Sat, Feb 03, 2007 at 07:54:17PM +0200 you wrote: Show instances are supposed to follow the convention that show x is a Haskell expression that recreates x. In other words, Show is mainly used for debugging, for simple serialization, and for interactive use in a Haskell shell like ghci or hugs. If you need to create strings from a datatype for some other reason, use a different function name. If you need to do it for several datatypes, create your own class. Yes, I think another Show-like class will probably be a better solution... Thanks Yitzchak and Bjorn, -- DoubleF No virus detected in this message. Ehrm, wait a minute... /kernel: pid 56921 (antivirus), uid 32000: exited on signal 9 Oh yes, no virus:) pgpKrflZnT8EB.pgp Description: PGP signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
