- Haskell-Cafe - Haskell.org

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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Int vs Integer?
by Daniel Carrera 05 May '05

05 May '05

Hello, What's the difference between "Int" and "Integer"? How can I tell Haskell which one I want? I'm having trouble with a function: ints = 0 : map (1+) ints prng = map iter ints where iter 0 = [0,0] iter n = [i,j] where i = mod n 256 j = ints !! i (eventually 'iter' will be more a more interesting function). When I try to load this module in Hugs I get the error: ERROR "./PRNG.hs":24 - Type error in list *** Expression : [i,j] *** Term : j *** Type : Integer *** Does not match : Int Line 24 is the 'prng' line. I've spent all day trying to fix this, but for the life of me I can't figure out why it happens or how to make it stop. Haskell just doesn't seem to like the 'iter !! i' construct. It's interesting that if you replace 'i' by (say) 3, Haskell runs the program happily. But, if you replace 'i = mod n 256' by 'i=3' you get the same error. Any words of wisdom would be appreciated. Cheers, Daniel.

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Where do you use Haskell?
by Daniel Carrera 05 May '05

05 May '05

Hi all, Again, I'm the new guy slowly learning this "fuctional programming" thing. :-) I've been reading, and I'm really liking the elgance of Haskell, and FP as a whole. But I wonder about the range of applicability. You see, one of the things about FP is that there are no side-effects and the same function on the same parameters always returns the same value. But any program that interacts with the real world cannot meet those properties. The function ask_user_name() will not return the same value each time. If write a chess program, the function get_user_move() will be different each time. And every time you update the screen, you're having a side-effect. So, I figure that to do these tasks you heed that "do ... <-" work around. But that kills the whole point of using FP in the first place, right? So, I'm tempted to conclude that FP is only applicable to situations where user interaction is a small part of the program. For example, for simulations. Now, I'm sure I'm not the first person to have this train of thought. And I'm sure there is a good answer why I'm wrong. :-) I'm eager to hear what that might be. Cheers, Daniel.

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Conal Elliott's Vertigo, anyone get it to run?
by Atwood, John Wesley 05 May '05

05 May '05

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/ John Atwood

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