Proposal: Strict scanl, scanl1 and mapAccumL

[Roman Cheplyaka]

* Henning Thielemann <lemming at henning-thielemann.de> [2012-11-12 13:25:56+0100]
> >In case your accumulator is a Map you really want to use foldl'.
> 
> Why not a deepseq foldl'?

First, you may actually want your Map to contain lazy values.

Second, you may know that your values are already evaluated, so
deepseq is just a waste of time. deepseq is far from being cheap, since 
it has to traverse the whole structure, regardless of what has been
already evaluated.

Roman