instance Applicative Data.Map

Henning Thielemann lemming at
Wed Nov 14 20:46:29 CET 2012

An ZipList-like Applicative instance for Data.Map would be nice. I have an 
application where I like to write
    liftA3 f amap bmap cmap
    Map.intersectionWith ($) (Map.intersectionWith f amap bmap) cmap

But I cannot complete the instance implementation because there is no 
sensible definition for 'pure' for Data.Map. :-(

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