Am Sonntag, 10. April 2005 17:33 schrieben Sie:

On 2005/04/10, at 18:18, Daniel Fischer wrote:

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But this returns [] and doesn't work. I can't get "left" to know that it is working with the rightmost element. It just throws away every element when its right hand side is empty.

I found a solution that works for Strings, but I am looking for a more general solution. This exercise may yet again be one of those that is difficult to solve with my current knowledge of Haskell, but I'm asking anyway.

I cannot imagine how you could do it for Strings, but not for general lists. Mind sending me the code?

The code is here: http://wiki.pragprog.com/cgi-bin/wiki.cgi/ThompsonNineAnswersJD Look for 9.13 towards the bottom of the page.

It uses chr 0 as an end of string marker, and so this solution only works for Strings.

Unfortunately, Strings may contain '\0': *Init> finit "this doesn't\0quite\0work\0!" "this doesn't\NULquite\NULwor" so it doesn't work in all cases. The idea is nice, though: import Data.Maybe finit = catMaybes . foldr f [Nothing] . map Just where f x ys = case ys of [Nothing] -> [] _ -> x:ys will do fine.

-- Kaoru Hosokawa khosokawa@gmail.com

Cheers, Daniel