Re: [Haskell-cafe] how to write a loop in haskell way

2010/12/19 Ivan Lazar Miljenovic :

On 19 December 2010 21:27, ender wrote:

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Hi all:      I'v been learning haskell for several months, and now I'm trying to write some "real word" program in haskell, like finding files under one directory or something      My problem is that, I dont know the way of writing a loop in haskell. I searched google and found some code that translate c loop into haskell like this one:

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I am new to haskell and would look to write a function equivalent to the following loop in C

int value = 500000; int part_stack[4]; int *part_ptr = part_stack; for (; value; value /= 10000)       *part_ptr++ = value % 10000;

part_stack :: [Int] part_stack = [0,50]

Note that I've performed a memoization optimization--this makes the code both smaller, faster and easier to read! :P

Ignore David, he's pulling your leg.  Here's the proper translation:

 do   alloca $ \value -> do   poke value (500000::Int)   allocaArray 4 $ \part_stack -> do   alloca $ \part_ptr -> do   poke part_ptr part_stack   let loop = do            val <- peek value            if val == 0 then return () else do            p <- peek part_ptr            poke p (val `rem` 10000)            poke part_ptr (p `plusPtr` 1)            poke value (val `quot` 10000)            loop   loop

and I really think that's not a "haskell way", it's just translate c code into haskell code byte by byte My question is: how to translate above c code into haskell in "haskell way"

Short answer: you don't.

Longer answer: have a read through http://book.realworldhaskell.org/read/io-case-study-a-library-for-searching-...

-- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com IvanMiljenovic.wordpress.com

Great! That's exactly what I want, thanks a lot