Improve heap-allocation in mergeWithKey'.
Improve heap-allocation in mergeWithKey'.

Avoid allocating the closure for local function 'merge'.

shockkolate/containers,hvr/containers,iu-parfunc/containers,ekmett/containers,shockkolate/containers,meiersi/psqueues-old,iu-parfunc/containers,Zigazou/containers,Zigazou/containers,Zigazou/containers,ekmett/containers,shockkolate/containers,iu-parfunc/containers,hvr/containers,hvr/containers,ekmett/containers