Re:Optimizing Guile Scheme
by Iceland_jack on Thursday September 26, 2024 @11:55AM
(#41659913)
lift = sequenceA @[] @(a ->)
[ Parent
| on HN ]
Did you do that by hand? I guessed you used the classic `pointfree` program, bit that gave
lift = fix ((`ap` tail) . (. head) . flip ((.) . liftM2 (:)))
As far as I know it's not possible to get this functionality in Haskell even with clever instance magic, but I'd love to be proved wrong.
Re:Optimizing Guile Scheme
by Iceland_jack on Saturday September 28, 2024 @04:47AM
(#41678890)
> As far as I know it's not possible to get this functionality in Haskell even with clever instance magic
It is possible to fill in basic function bodies based on their type, using ghc-justdoit (https://hackage.haskell.org/package/ghc-justdoit). That's maybe not what you meant, if you are looking for integrating pointfree into Haskell it can be added to ghci or your development environment.
foo :: ((a -> r) -> r) -> (a -> ((b -> r) -> r)) -> ((b -> r) -> r)
foo = (…)
In this case I wrote it because I knew about the pattern. Your lift definition is just ($) flip \a -> ($ a)
= flip (&)
= flip (flip ($))
= ($)
Re:Optimizing Guile Scheme
by Iceland_jack on Saturday September 28, 2024 @04:52AM
(#41678910)
Maybe you meant to write
(??) :: Functor f => f (a -> b) -> a -> f b
funs ?? a = fmap ($ a) funs
from lens: https://hackage.haskell.org/package/lens-5.3.2/docs/Control-...This is valid definition of lift along a different, less interesting but more general axis.
lift = (??) @[]