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

[ender]

2010/12/19 Ivan Lazar Miljenovic <ivan.miljenovic at gmail.com>:
> On 19 December 2010 21:27, ender <crazyender at gmail.com> wrote:
>> 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:
>>
>>> > > 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-the-filesystem.html
>
> --
> Ivan Lazar Miljenovic
> Ivan.Miljenovic at gmail.com
> IvanMiljenovic.wordpress.com
>

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