[Haskell-cafe] Map unionWith generalization

Twan van Laarhoven twanvl at gmail.com
Wed Jan 27 21:09:49 EST 2010

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


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