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Diffstat (limited to 'libraries/base/Control/Arrow.hs')
| -rw-r--r-- | libraries/base/Control/Arrow.hs | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/libraries/base/Control/Arrow.hs b/libraries/base/Control/Arrow.hs index b723dd4722..f6067a01c3 100644 --- a/libraries/base/Control/Arrow.hs +++ b/libraries/base/Control/Arrow.hs @@ -304,11 +304,19 @@ newtype ArrowMonad a b = ArrowMonad (a () b) instance Arrow a => Functor (ArrowMonad a) where fmap f (ArrowMonad m) = ArrowMonad $ m >>> arr f +instance Arrow a => Applicative (ArrowMonad a) where + pure x = ArrowMonad (arr (const x)) + ArrowMonad f <*> ArrowMonad x = ArrowMonad (f &&& x >>> arr (uncurry id)) + instance ArrowApply a => Monad (ArrowMonad a) where return x = ArrowMonad (arr (\_ -> x)) ArrowMonad m >>= f = ArrowMonad $ m >>> arr (\x -> let ArrowMonad h = f x in (h, ())) >>> app +instance ArrowPlus a => Alternative (ArrowMonad a) where + empty = ArrowMonad zeroArrow + ArrowMonad x <|> ArrowMonad y = ArrowMonad (x <+> y) + instance (ArrowApply a, ArrowPlus a) => MonadPlus (ArrowMonad a) where mzero = ArrowMonad zeroArrow ArrowMonad x `mplus` ArrowMonad y = ArrowMonad (x <+> y) |