Andrea Rossato
On Mon, Sep 18, 2006 at 04:16:55AM -0700, Carajillu wrote:
Wow! I'm starting to love this languaje, and the people who uses it!:)
You spoke too early. My code had a bug, a huge one...
this is the right one:
-- Replaces a wildcard in a list with the list given as the third argument substitute :: Eq a => a -> [a] -> [a] -> [a] substitute e l1 l2= [c | c <- check_elem l1] where check_elem [] = l1 check_elem (x:xs) = if x == e then (l2 ++ xs) else [x] ++ check_elem xs
I think it's nicer to do it like this: substitute e l l' = concat (map subst_elem l) where subst_elem x | x == e = l' | otherwise = [x] since "subst_elem" has a more straightforward meaning than "check_elem", and the concatenation is handled by a well known standard function. Also, it would usually be more useful to have the argument to replace /with/ before the argument to replace /in/, so that ("substitute '*' "wurble") is a function that replaces all the '*'s in it's argument with "wurble"s. And if you do that, you can write it like this: subst e l' = concat . map subst_elem where subst_elem x | x == e = l' | otherwise = [x] -- Jón Fairbairn Jon.Fairbairn@cl.cam.ac.uk