Add stricter accumulating map

[David Feuer]

mapAccumL is a generally useful operation on Traversable containers. The
only version currently offered uses (a copy of) lazy state to support
streaming left-to-right consumption. This does not, however, seem terribly
appropriate/efficient for other usage patterns (e.g., a FIFO queue with
right view, or a Map). Could we add a version that uses a copy of
Control.Monad.Trans.State.Strict to support those too?
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/libraries/attachments/20151024/3e12e333/attachment.html>