Lysxia/first-class-families
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Define Case_ with an explicit family for equality instead of implicitly through pattern-matching

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Lysxia 2020-03-08 11:13:37 -04:00
parent 464d78da85
commit fe527778ae
1 changed files with 2 additions and 2 deletions
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src/Fcf/Utils.hs
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@ -33,6 +33,7 @@ import Data.Type.Bool (If)
import GHC.TypeLits (Symbol, TypeError, ErrorMessage(..))
import Fcf.Core
import Fcf.Combinators (Pure)
-- | Type-level 'error'.
data Error :: Symbol -> Exp a
@ -110,8 +111,7 @@ data Case :: [Match j k] -> j -> Exp k
type instance Eval (Case ms a) = Case_ ms a
type family Case_ (ms :: [Match j k]) (a :: j) :: k where
Case_ ('Match_ a b : _ ) a = b
Case_ ('Match_ _ _ : ms) a = Case_ ms a
Case_ ('Match_ a' b : ms) a = Eval (If (TyEqImpl a' a) (Pure b) (Case ms a))
Case_ ('Is_ p b : ms) a = Case_ [ 'True --> b
, 'False --> Case_ ms a
] (p @@ a)