(1) what is the "more useful Kleisli composition" and what would be "less useful" ?
This type signature (Int -> (Integer->r) -> r) -> (Integer -> (String -> r) -> r) -> (Int -> (String -> r) -> r) is the Cont monad instantiation of (>=>) :: Monad http://hackage.haskell.org/package/base-4.9.0.0/docs/Control-Monad.html#t:Mo... m => (a -> m b) -> (b -> m c) -> a -> m c See http://hackage.haskell.org/package/base-4.9.0.0/docs/ Control-Monad.html#v:-62--61--62- Being more uniform, this signature is more useful than the one you had earlier worked with: combine :: Int -> (Int -> (Integer->r) -> r) -> -- f1 (Integer -> (String -> r) -> r) -> -- f2 ((String -> r) -> r)
Now my 'combine' function seems to be different from 'bind' (>>=). It also just too simple to be true.
You got Kleisli composition, although not monadic bind. That's still a win
of sorts.
Best, Kim-Ee Yeoh
On Monday, August 8, 2016, martin
Am 08/07/2016 um 05:18 PM schrieb Kim-Ee Yeoh:
Have you heard of Djinn?
https://hackage.haskell.org/package/djinn
If you punch in the signature of the combine function you're looking for (rewritten more usefully in Kleisli composition form):
(Int -> (Integer->r) -> r) -> (Integer -> (String -> r) -> r) -> (Int -> (String -> r) -> r)
Thanks for pointing out Djinn, but I want to understand. And there are a number of things I don't understand. Maybe you can help me out:
(1) what is the "more useful Kleisli composition" and what would be "less useful" ?
(2) I was hoping my experiments would eventually make the Cont monad appear and I originally even named my combinator 'bind' instead of 'combine'. My hope was fueled by the observation that
combine a f g = f a g
works with f substitued with f1 :: Int -> (Integer->r) -> r and g substitued with f2 :: Integer -> (String -> r) -> r
As a next step I would have wrapped (b->r) -> r in a newtype C r b and my functions f1 and f2 would have had the types
f1 :: Int -> C r Integer f2 :: Integer -> C r String
Now my 'combine' function seems to be different from 'bind' (>>=). It also just too simple to be true.
Somwhere I am making a fundamental mistake, but I cannot quite see it.
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