flip -package:cabal-install-solver package:MissingH
Flips an association list. Converts (key1, val), (key2, val) pairs to
(val, [key1, key2]).
Flips a Map. See
flipAL for more on the similar function for
lists.
Returns a list of all keys in the Map whose value matches the
parameter. If the value does not occur in the Map, the empty list is
returned.