Andrea Rossato <[EMAIL PROTECTED]> writes:
> 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 [EMAIL PROTECTED]
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