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Add HasField instances for hlists.

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This commit is contained in:
Rob Rix 2016-06-16 11:52:14 -04:00
parent eb91962cbb
commit 3b8c1546a5
1 changed files with 9 additions and 0 deletions
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src/Data/Record.hs
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@ -23,3 +23,12 @@ type a :=> b = Tagged a b
-- | This has type a :=> b. When you require a to be some concrete type (and you usually will), it should be provided by context, whether using ascription, a type signature for the binding, `asTypeOf`, or some other way to allow the specific type to be inferred. -- | This has type a :=> b. When you require a to be some concrete type (and you usually will), it should be provided by context, whether using ascription, a type signature for the binding, `asTypeOf`, or some other way to allow the specific type to be inferred.
field :: b -> a :=> b field :: b -> a :=> b
field = Tagged field = Tagged
-- Instances
instance {-# OVERLAPPABLE #-} HasField fields field => HasField (notIt ': fields) field where
getField (RCons _ t) = getField t
instance {-# OVERLAPPABLE #-} HasField (field ': fields) field where
getField (RCons h _) = h