Add scanl'

The presence of foldl' and foldl1' suggests the addition of scanl' (and scanl1') to Data.List:

scanl'                   :: (a -> b -> a) -> a -> [b] -> [a]
scanl' f q ls            =  q `seq` (q : (case ls of
                                     []   -> []
                                     x:xs -> scanl' f (f q x) xs))

This would finally sort out the infamous (last . scanl) problem.

Trac metadata

Trac field	Value
Version	7.7
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries/base
Test case
Differential revisions
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CC	mail@nh2.me
Operating system
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