Name Rascal/Expressions/Values/Map/Union

Synopsis Union of two maps.

Syntax Exp1 + Exp2

Types

Exp1	Exp2	Exp1 + Exp2
map[TK1, TV1]	map[TK2, TV2]	map[lub(TK1,TK2),lub(TK1,TK2) ]

Description The result is the union of the two map values of Exp1 and Exp2. If they have a pair with the same key in common, that key will be associated in the union with the value associated with that key in Exp2.

Examples

rascal>("apple": 1, "pear": 2) + ("banana": 3, "kiwi": 4);
map[str, int]: ("banana":3,"pear":2,"kiwi":4,"apple":1)
rascal>("apple": 1, "pear": 2) + ("banana": 3, "apple": 4);
map[str, int]: ("banana":3,"pear":2,"apple":4)

Benefits Map union is very suited for representing environment composition in interpreters.

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