Re: [Haskell-cafe] Problems interpreting

Definitely I'll take this solution, I'm reading about Pointfree, I think it's not that dificult to understand. And moreover it's the simpliest way to write code. Jón Fairbairn-2 wrote:

Andrea Rossato writes:

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On Mon, Sep 18, 2006 at 04:16:55AM -0700, Carajillu wrote:

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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

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