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NY Functional Programmers Network: F# Talk by Don Syme, Monday De cember 10th at 7pm
by Mansell, Howard 04 Dec '07

04 Dec '07

Credit Suisse will be hosting a talk by Don Syme from Microsoft Research on Monday December 10th. He will talk about F# and Microsoft's plans for it. This talk is arranged by the New York Functional Programmers Network, a group of individuals in the New York area who are interested in functional programming. Many of us also use functional programming in our work life. Despite the URL below, we are typically interested in statically typed functional languages. If you are interested in coming, please RSVP at the meetup site below: http://lisp.meetup.com/59/ <http://lisp.meetup.com/59/> Regards Howard Mansell Global Modelling & Analytics Group Credit Suisse ============================================================================== Please access the attached hyperlink for an important electronic communications disclaimer: http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html ==============================================================================

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Nofib modifications
by Neil Mitchell 04 Dec '07

04 Dec '07

Hi, Some of the nofib suite are messed up by Yhc/nhc because of the monomorphism restriction. Take imaginary/bernouilli as an example: powers = [2..] : map (zipWith (*) (head powers)) powers Hugs and GHC both see powers :: [[Integer]] and a CAF. Yhc (and nhc) both see powers :: (Enum a, Num a) => [[a]] and no CAF. This completely destroys the performance in Yhc/nhc. Since this is not so much a performance aspect but a compiler bug, based on a feature whose future in Haskell' is as yet unclear, perhaps it would be wise to patch nofib to include an explicit type signature where this matters. I am happy to send in a patch (or just apply it) - but I have no idea who "maintains" the suite. I've CC'd those people who make substantial use of the nofib suite. Thanks Neil

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isSpace
by Ryan Bloor 04 Dec '07

04 Dec '07

HI I will try and explain it better. I am meaning to write a function that takes a string, " apple" and eliminates the spaces at the start ONLY. called........ removeSpace :: String -> String I decided to use the function 'dropWhile' and another one 'isSpace' in the 'removeSpace' function. removeSpace:: String -> String removeSpace a = case dropWhile isSpace a of "" -> I get stuck here... I am not sure how to go about this function. Any ideas. Ryan _________________________________________________________________ The next generation of MSN Hotmail has arrived - Windows Live Hotmail http://www.newhotmail.co.uk

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Advice for clean code.
by David McBride 04 Dec '07

04 Dec '07

I am still in the early stages learning haskell, which is my first foray into functional programming. Well there's no better way to learn than to write something, so I started writing a game. Mostly the thing looks good so far, far better than the C version did. However, my problem is that code like the following is showing up more often and it is becoming unwieldy. gameLoop :: World -> IO () gameLoop w = do drawScreen w action <- processInput let (result, w') = processAction action w case result of MoveOutOfBounds -> putStrLn "Sorry you can't move in that direction." MoveBadTerrain a -> case a of Wall -> putStrLn "You walk into a wall." Tree -> putStrLn "There is a tree in the way." otherwise -> putStrLn "You can't move there." otherwise -> return () let w'' = w' { window = updateWindowLocation (window w') (location $ player w')} unless (action == Quit) (gameLoop w'') Where world contains the entire game's state and so I end up with w's with multiple apostrophes at the end. But at the same time I can't really break these functions apart easily. This is error prone and seems pointless. I have been reading about control.monad.state and I have seen that I could run execstate over this and use modify but only if each function took a world and returned a world. That seems really limiting. I'm not even sure if this is what I should be looking at. I am probably just stuck in an imperative mindset, but I have no idea what to try to get rid of the mess and it is only going to get worse over time. Any suggestions on what I can do about it?

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Haskell interface file (.hi) format?
by Rob Hoelz 04 Dec '07

04 Dec '07

Hello fellow Haskellers, Does anyone know if/where I can find a specification for the .hi files generated by GHC? I ask because I want to write an omni-completion plugin for Vim to make Haskell hacking a bit nicer. Thanks, Rob Hoelz

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Re: [Haskell] IVars
by Bertram Felgenhauer 04 Dec '07

04 Dec '07

[redirecting to haskell-cafe] Simon Peyton-Jones wrote: > But since the read may block, it matters *when* you perform it. For > example if you print "Hello" and then read the IVar, you'll block > after printing; but if you read the IVar and then print, the print > won't come out. If the operation was pure (no IO) then you'd have > a lot less control over when it happened. Well, the same can happen with any pure computation that does not terminate. It's the compiler's job to avoid that, and as far as I know ghc is pretty careful not to reorder pure computations and IO operations too much. I'd argue for adding both an IO and a pure version of readIVar to an IVar implementation. Both have their uses; the firts gives you a little extra control, while the second one can easily be evaluated on demand, at the risk of creating a mine field of potential deadlocks. Bertram

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regexen no go with 6.8.1?
by Jason Dusek 04 Dec '07

04 Dec '07

Is it just me, or are all the regex implementations broken with new change in lib layout for 6.8.1? Are fixes available in darcs? -- _jsn

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Leopard: ghc 6.8.1 and the case of the missing _environ
by Joel Reymont 04 Dec '07

04 Dec '07

Symptoms: You build 6.8.1 from source on Leopard (x86 in my case) and then junior:ghc-6.8.1 joelr$ ghci GHCi, version 6.8.1: http://www.haskell.org/ghc/ :? for help ghc-6.8.1: /usr/local/lib/ghc-6.8.1/lib/base-3.0.0.0/HSbase-3.0.0.0.o: unknown symbol `_environ' Loading package base ... linking ... ghc-6.8.1: unable to load package `base' Problem: ghc binaries are being stripped upon installation which eliminates _environ, e.g. junior:tmp joelr$ nm x|grep environ 00002ff0 T ___hscore_environ 0004d004 D _environ junior:tmp joelr$ strip x junior:tmp joelr$ nm x|grep environ Solution: Need to make sure install-sh does _not_ use the -s option. Haven't found out where this needs to be done yet. A temporary workaround is to ask Manuel for the pre-built binaries. Thanks, Joel -- http://wagerlabs.com

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Re: The Opposite of $
by Alan Hawkins 04 Dec '07

04 Dec '07

|> is not defined in the prelude but can be defined as let (|>) = flip ($) to make it the opposite of $ which means the syntax looks more like the Unix pipe '|' command eg. filter (\x-> x >3 && x < 7) $ [1..10] ++ [5] [1..10] ++ [5] |> filter (\x-> x >3 && x < 7) res: [4,5,6] note that with the |> the function applications are read as naturally left to right as apposed to the $ which reads left to right. a style more in line with the syntax f (x) ____________________________________________________________________________________ Never miss a thing. Make Yahoo your home page. http://www.yahoo.com/r/hs

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The Opposite of $
by PR Stanley 04 Dec '07

04 Dec '07

Hi According to the Haskell Wikibook the is the opposite of $. The text also oints out that the "|>" can be used as a substitute. I tried using |> but to no avail. Is the list au fait with the |> operator? Thanks, Paul

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