Cale Gibbard wrote:
Indeed, I agree.
While we're at it, I'd like to see the Arrow class a bit more thinly
sliced. Something like this:
class Compositor a where
identity :: a b b
(>>>) :: a b c -> a c d -> a b d
class Compositor a => Arrow a where
pure :: (b -> c) -> a b c
class Arrow a => ArrowProduct a where
(&&&) :: a b c -> a b c' -> a b (c, c')
-- derived:
first :: a b c -> a (b, d) (c, d)
second :: a b c -> a (d, b) (d, c)
(***) :: a b c -> a b' c' -> a (b, b') (c, c')
class Arrow a => ArrowCoproduct a where
(|||) :: a b d -> a c d -> a (Either b c) d
-- derived:
left :: a b c -> a (Either b d) (Either c d)
right :: a b c -> a (Either d b) (Either d c)
(+++) :: a b c -> a b' c' -> a (Either b b') (Either c c')
class (ArrowProduct a,ArrowCoproduct a) => ArrowFull a
etc.
--
Ashley Yakeley
Seattle WA
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