Haskell Language Containers - Data.Map Monoid instance
Example
Map k v provides a Monoid instance with the following semantics:
memptyis the emptyMap, i.e. the same asMap.emptym1 <> m2is the left-biased union ofm1andm2, i.e. if any key is present both inm1andm2, then the value fromm1is picked form1 <> m2. This operation is also available outside theMonoidinstance asMap.union.
