Xtykutl

So I've figured this out non-recursively like this:

noSpaces :: [Char] -> [Char]    

noSpaces xs = [f | r <- xs, f <- if (r == ' ') then "%20" else [r]]

but now i need to figure out how to do that recursively, with no pattern matching and no concatenation...

I figured out other recursive functions (gcd, fib, and a couple others involving numbers) easily enough... but am lost on this for some reason and getting lost-er the more stuff i try that doesn't work...

I found the other answer on here about doing this in Haskell... but that idea uses two separate functions, one being like a helper function -- how would you go about this all in one function, as concisely as possible?

something like:

replace [Char] = [Char]

replace (x:xs)

    | x == ' ' = "%20":replace xs

which compiles but of course i get the 'non-exhaustive patterns in function' error message, and can't figure out what to put in the 'otherwise' clause...

any help would be appreciated!

You miss the case where it is not a ' '.
So, try this:

replace  = 

replace (x:xs) 

    | x == ' ' = "%20" ++ replace xs

    | otherwise = x : replace xs

You need to use ++ in your first guard because a string is a list of chars.

Try this

replace      = 

replace (x:xs) = (if x == ' ' then "%20" else [x]) ++ replace xs