Exactly! I'd be disappointed to see (.:) get enshrined in the base when
it's such a special case: just one functor ((->) a), just one class
(Functor), and just two levels deep. Once people learn the general
patterns, they're easy to read & write and *much* more general & flexible.
See http://conal.net/blog/posts/semantic-editor-combinators and the lens
libraries.
-- Conal
On Wed, Aug 17, 2016 at 2:14 PM, Tony Morris
You'd generalise it to:
fmap . fmap :: (Functor f, Functor g) => (a -> b) -> f (g a) -> f (g b)
And then, would you do the same for Traversable, Foldable and Applicative?
On 18/08/16 03:43, Alex Belanger wrote:
Hi,
Some of you might be familiar with (.:) = (.) . (.).
It has type :: (c -> d) -> (a -> b -> c) -> a -> b -> d
It allows the composition of two functions, the first one, accepting one operand, and the second, two operands.
This appears to be a very common pattern, referenced a bit everywhere, almost always defined on lambdabot and found in multiple codebases in the wild.
I'd like the know the general sentiment about this operator, as well as how its inclusion in base, probably Data.Function, would be perceived before I actually try to make it happen.
Cheers, Alex (nitrix).
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