Re: [Haskell-cafe] Pattern matching does not work like this?

On Wed, Jul 15, 2009 at 3:08 AM, Hans Aberg wrote:

On 15 Jul 2009, at 12:25, Eugene Kirpichov wrote:

If ++ could be pattern matched, what should have been the result of

...

"let (x++y)=[1,2,3] in (x,y)"?

It will branch. In terms of unification, you get a list of substitutions.

f :: [a] -> ([a],[a]) f (x ++ y) = (x,y) If this pattern branches, it could hardly be considered a *function *which takes lists and returns pairs. It would have to return something else. Luke