[Haskell-cafe] Folding Integrals

[Reinier Lamers]

Mattias Bengtsson wrote:

>I found myself writing this for an Euler-problem:
>
>  
>
>>digits :: Int -> [Int]
>>digits i | i < 10    = [i]
>>         | otherwise = i `mod` 10 : digits ( i `div` 10 )
>>    
>>
>
>And i realised it was quite some time ago (before this function) i had
>actually written any explicitly recursive function. 
>
Back in my Introduction to Functional Programming course, Daan Leijen 
demonstrated how to print integers in Haskell using function 
composition. Something along the lines of:

printint :: Int -> [Char]
printint = map chr . map (+0x30) . reverse . map (`mod` 10) . takeWhile 
(>0) . iterate (`div`10)

You can easily translate a number to a list of digits without explicit 
recursion.

Regards,
Reinier