May 2005 - Haskell-Cafe

Newbie : What does the sequence function make?
by mandziy＠web.de 06 May '05

06 May '05

Please,can anyone explain it to me? Cheers! ______________________________________________________________ Verschicken Sie romantische, coole und witzige Bilder per SMS! Jetzt bei WEB.DE FreeMail: http://f.web.de/?mc=021193

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supplying some of the arguments to a function
by Mark Goldman 06 May '05

06 May '05

if I had a function f that took x y and z in that order, is there some way that I can supply y and z and get back a function that takes x? This question comes about after talking with a prof about currying and wether it buys you anything. -mdg

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where versus let
by Scott J. 06 May '05

06 May '05

Hi, Instead of the following piece of code : data State s a = S(s -> (a,s)) instance Monad (State s) where return a = S(\s -> (a,s)) (S f ) >>= g = S(\s -> let (a,s1) = f s S fun = g a (b,s2) = fun s1 in (b,s2) ) I thought to write it in the following form using "where": data State s a = S(s -> (a,s)) instance Monad (State s) where return a = S(\s -> (a,s)) (S f ) >>= g = S(\s -> (b,s2) where (a,s1) = f s S fun = g a (b,s2) = fun s1 ) However the compiler does not accept this use of "where". What is the reason? Thanks Jan

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I love type declarations. :-)
by Daniel Carrera 06 May '05

06 May '05

Hey, Whooo hoo! I just finished my first non-trivial Haskell program. It's the pseudo-random number generator from RC4. And if it weren't for type declarations I'd still be bug-hunting. I've been trying to get the PRNG to work for two days, but Hugs kept wanting to use Integer where Int should be used, ugh. But while reading a Haskell tutorial I came accross type declarations: function :: Int -> Int -> [Int] This solved all my problems! I added proper type declarations to everything, and suddenly Hugs was happy. Type declarations also brought other benefits: 1) I quickly spoted two bugs I hadn't hit yet. 2) I removed the fromIntegral() functions, making the code cleaner. 3) And my code is self-documented. Before, when writing imperative code, I would add a comment for each function describing its input and output. Now type declarations provide that, so I merely describe what the function does. And type declarations are better than a comment because Haskell helps me make sure that they are right. Go Haskell! Cheers, Daniel.

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How to get an variable or its value?
by Michael Onofruk 06 May '05

06 May '05

Hi! >From this "monster" [([Int],Char)] I need to get Char variable. How do I do this? Or in general - how does this works in Haskell? Cheers, M. Yahoo! Mail Stay connected, organized, and protected. Take the tour: http://tour.mail.yahoo.com/mailtour.html

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RE: [Haskell-cafe] Conal Elliott's Vertigo, anyone get it to run?
by Atwood, John Wesley 05 May '05

05 May '05

> On 5/5/05, Atwood, John Wesley <john.atwood(a)hp.com> wrote: > > I tried to run Conal Elliott's Vertigo demos, on 3 diffferent XP > > boxes; it ran on none. The error is "Common Language Runtime Services > > - Appication has generated an exception that could not be handled. > > Process id=xxxx, Thread id=xxxx". Any suggestions? > > http://conal.net/Vertigo/ > > > On 5/5/05, Sebastian Sylvan [mailto:sebastian.sylvan@gmail.com] wrote: > Do you have .Net installed? > > I got it to run, don't know what you're doing wrong. > Yep, version 1.1; don't have the C# compiler installed, but it's my understanding that that's not needed for the demos. John

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Haskell vs OCaml
by Daniel Carrera 05 May '05

05 May '05

Hey, Marcin just mentioned OCaml as another functional programming language I should keep in mind. Can anyone offer an opinion on how Haskell and OCaml compare? Is OCaml as easy to learn as Haskell? Does it have much the same virtues? I'll go take a look at it. /daniel goes to Google. Cheers, Daniel.

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Re: [Haskell-cafe] How to show a variable with "show"?
by Michael Onofruk 05 May '05

05 May '05

> > > > And how do I see functions or variables defined > > inside of other functions? In example above - y > > > > Short answer -- you don't. > Thanks for explanations! Cheers, M. __________________________________ Do you Yahoo!? Yahoo! Mail - Helps protect you from nasty viruses. http://promotions.yahoo.com/new_mail

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Re: [Haskell-cafe] How to show a variable with "show"?
by Michael Onofruk 05 May '05

05 May '05

> module Main where > > main = do putStr (show (foo 3)) > putStr "\n" > putStr (show (foo 7)) > putStr "\n" > putStr (show y) > > foo x = (x + 2) / y where > y = 2 * 2 And how do I see functions or variables defined inside of other functions? In example above - y Yahoo! Mail Stay connected, organized, and protected. Take the tour: http://tour.mail.yahoo.com/mailtour.html

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How to show a variable with "show"?
by Michael Onofruk 05 May '05

05 May '05

Hi! In my program I would like to see an result of function or an variable. Wenn I use "show myfunction" or "show variable", I'm getting errors like "ERROR - Improperly terminated character constant" or " Syntax error in declaration (unexpected `;', possibly due to bad layout)" Any help would be appreciated! Yahoo! Mail Stay connected, organized, and protected. Take the tour: http://tour.mail.yahoo.com/mailtour.html

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