mightybyte/map-syntax — pull request #2 by ImAlsoGreg (2014-06-04 19:18:27+00:00)
Title: Add props and test cases using mapK and mapV

May have found a mapK bug, it seems that:

runMapSyntax M.lookup M.insert $ do { foo ; mapK (++"a") bar} == runMapSyntax M.lookup M.insert $ do { mapK (++"a" bar) }

(looking into that now).

For another example, try this: https://gist.github.com/ImAlsoGreg/98092ade3a086b14d356