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-module(maps_guard_update).
-export([test/0]).
test() ->
error = map_guard_update(#{},#{}),
first = map_guard_update(#{}, #{x=>first}),
second = map_guard_update(#{y=>old}, #{x=>second,y=>old}),
third = map_guard_update(#{x=>old,y=>old}, #{x=>third,y=>old}),
ok.
map_guard_update(M1, M2) when M1#{x=>first} =:= M2 -> first;
map_guard_update(M1, M2) when M1#{x=>second} =:= M2 -> second;
map_guard_update(M1, M2) when M1#{x:=third} =:= M2 -> third;
map_guard_update(_, _) -> error.
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