[Haskell-cafe] Java or C to Haskell

[Donald Bruce Stewart]

crespi.albert:
> 
> I'm trying to write in Haskell a function that in Java would be something
> like this:
> 
> char find_match (char[] l1, char[] l2, char e){
> 	//l1 and l2 are not empty
> 	int i = 0;
> 	while (l2){
> 		char aux = l2[i];
> 		char[n] laux = l2;
> 		while(laux){
> 			int j = 0;
> 			if(laux[j] = aux) laux[j] = e;
> 				j++;
> 		}
> 		if compare (l1, laux) return aux;
> 		else i++;
> 	}
> return '';
> }

Yikes!

> 
> compare function just compares the two lists and return true if they are
> equal, or false if they are not.
> it is really a simple function, but I've been thinking about it a lot of
> time and I can't get the goal. It works like this:
> 
> find_match "4*h&a" "4*5&a" 'h' ----> returns '5' (5 matches with the h)
> find_match "4*n&s" "4dhnn" "k" ----> returns ''  (no match at all - lists
> are different anyway)

That's almost a spec there :)

How about:

  import Data.List
 
  findMatch s t c
      | Just n <- elemIndex c s = Just (t !! n)
      | otherwise               = Nothing

Using it in GHCi:

> findMatch "4*h&a" "4*5&a" 'h'
Just '5'

> findMatch "4*n&s" "4dhnn" 'k'
Nothing

-- Don