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Define a Monoid instance for Assignment.

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Rob Rix 2017-09-01 09:58:54 -04:00
parent ddb5518878
commit d06927f604
1 changed files with 4 additions and 0 deletions
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src/Data/Syntax/Assignment.hs
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@ -333,6 +333,10 @@ makeState = State 0 (Info.Pos 1 1) []
-- Instances
instance (Enum grammar, Eq (ast (AST ast grammar)), Ix grammar) => Monoid (Assignment ast grammar a) where
mempty = empty
mappend = (<|>)
instance (Enum grammar, Eq (ast (AST ast grammar)), Ix grammar) => Alternative (Assignment ast grammar) where
empty :: HasCallStack => Assignment ast grammar a
empty = tracing (Alt []) `Then` return