September 2009 - Beginners

function - argument termination problem
by Γιάννης Μαντζουράτος 02 Sep '09

02 Sep '09

Hello, Is it possible to implement in haskell a function f (A) such that if A does not ever terminate then f always terminates, and if A always terminates then f does not ever terminate? I've been thinking it for a while, with no results unfortunately. the actual problem is that i can think of no way to force both ifs: a function that always terminates independently from its argument could be f (a) = 1, and a function that does not terminate even if its argument terminates could be: f (a) = f (a + 1), but i can't figure out a "hybrid" version... Is there any idea on this? Thanks in advance :-), yannis

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Using FiniteMap in ghci
by KwangYul Seo 02 Sep '09

02 Sep '09

Hello, I tried to load FiniteMap module in ghci and encountered an error message like the following: Prelude> import FiniteMap Could not find module `FiniteMap': it is a member of package ghc-6.8.2, which is hidden The error message says that it is hidden. How can I use the FiniteMap? Regards, Kwang Yul Seo

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Utter Newbie - simple problems, output - GHC vs GHCi
by Nigel Rantor 02 Sep '09

02 Sep '09

I am trying to get my head around Haskell but seem to keep butting against problems that have nothing to do with FP yet, but are simply to do with not understanding the tools. I've been trying a lot of code from multiple tutorials but I keep finding that the code simply does not work out of the box, and requires some other setup I am unaware of. I am currently on Debian, using GHC 6.8.2 installed using apt, so I assume that the toolchain is installed and working correctly. For example, the most recent tutorial I've been looking at is the "yet another haskell tutorial", here - http://www.cs.utah.edu/~hal/docs/daume02yaht.pdf One of the exercises after talking about functions that act on lists is to determine the number of lowercase letters in a string. Fine, that makes complete sense to me. I figure something along the lines of: length( filter( Char.isLower "LoweR" ) ) should return the value 3 If I attempt this at the interactive GHC prompt I get the following: ------------------------------------------------------------------------------------------ wiggly@mink:~/src/ht$ ghci GHCi, version 6.8.2: http://www.haskell.org/ghc/ :? for help Loading package base ... linking ... done. Prelude> show( length( filter( Char.isLower "LoweR" ) ) ) <interactive>:1:35: Couldn't match expected type `Char' against inferred type `[Char]' In the first argument of `GHC.Unicode.isLower', namely `"LoweR"' In the first argument of `filter', namely `(GHC.Unicode.isLower "LoweR")' In the first argument of `length', namely `(filter (GHC.Unicode.isLower "LoweR"))' Prelude> ------------------------------------------------------------------------------------------ If I attempt to put the code into a file and compile it I get the following: [Code] ------------------------------------------------------------------------------------------ module Main where import Char main = show( length( filter( Char.isLower "LoweR" ) ) ) ------------------------------------------------------------------------------------------ [Terminal] ------------------------------------------------------------------------------------------ wiggly@mink:~/src/ht$ ghc -o test ex3.hs ex3.hs:3:42: Couldn't match expected type `Char' against inferred type `[Char]' In the first argument of `isLower', namely `"LoweR"' In the first argument of `filter', namely `(isLower "LoweR")' In the first argument of `length', namely `(filter (isLower "LoweR"))' wiggly@mink:~/src/ht$ ------------------------------------------------------------------------------------------ This is one of the smallest examples I can think of posting for some help, and quite frankly, I'm feeling a bit dim because I just cannot understand why this doesn't work...I've tried in vain to mess with the code (I won't attempt to describe it, I'm not au fait enough with Haskell terminology yet, it would sound like gibberish *and* be incorrect) Any help would be awesome, equally, any ready-to-run examples/tutorials that people could recommend would likewise be awesome and beer-worthy[0]. Cheers, n [0] offer only applies to those in the London area or those environs where I find myself randomly

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haskell code to html
by I. J. Kennedy 31 Aug '09

31 Aug '09

Is there a decent utility out there for syntax coloring haskell code?(haskell to html)

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