Apply two functions on corresponding values in a pair, where the
pattern match on the pair constructor is lazy. This is crucial in
recursions such as the one of partition
. One the other hand
there are applications where strict application is crucial, e.g.
mapSnd f ab
where the left pair member is a large lazy list.
With the lazy mapSnd
we make the application of f
depend on the whole pair ab
. See Data.Tuple.Example
for two examples where one variant is definitely better than the other