[Haskell-cafe] Map unionWith generalization

[Twan van Laarhoven]

Hans Aberg wrote:
> For example, in Map String Integer (sparse representation of monomials) 
> compute the minimum value of all associative pairs with the same key 
> (the gcd); if only one key is present, the absent should be treated as 
> having value 0. So
>   unionWith min xs ys
> will not work, because unionWith will always apply the identity to the 
> remaining value when one key is missing, whereas it should be sent to 0.

If missing keys represent 0, then wouldn't this work?

     intersectionWith min xs ys


Twan