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📝 the Eval instance for Union.

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Rob Rix 2017-12-21 11:46:00 -05:00
parent 2044714a5a
commit c6e086d208
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src/Data/Abstract/Eval.hs
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@ -29,6 +29,7 @@ class Monad m => Eval term v m constr where
default eval :: (MonadFail m, Show1 constr) => ((v -> m v) -> term -> m v) -> ((v -> m v) -> constr term -> m v) default eval :: (MonadFail m, Show1 constr) => ((v -> m v) -> term -> m v) -> ((v -> m v) -> constr term -> m v)
eval _ _ expr = fail $ "Eval unspecialized for " ++ liftShowsPrec (const (const id)) (const id) 0 expr "" eval _ _ expr = fail $ "Eval unspecialized for " ++ liftShowsPrec (const (const id)) (const id) 0 expr ""
-- | If we can evaluate any syntax which can occur in a 'Union', we can evaluate the 'Union'.
instance (Monad m, Apply (Eval t v m) fs) => Eval t v m (Union fs) where instance (Monad m, Apply (Eval t v m) fs) => Eval t v m (Union fs) where
eval ev yield = apply (Proxy :: Proxy (Eval t v m)) (eval ev yield) eval ev yield = apply (Proxy :: Proxy (Eval t v m)) (eval ev yield)