Arbitrary function sections

[a0s]

For operators we have the following shorthand:

op :: a -> b -> c
(`op` y) === \x -> x `op` y
(x `op`) === \y -> x `op` y

It would be nice to have a similar facility for
functions, e.g.:

f :: a -> b -> c -> d -> e
f _ y _ t === \x z -> f x y z t
f x _ z _ === \y t -> f x y z t
f x _ z === \y -> f x y z === \y t -> f x y z t

Because "_" is currently not allowed as an identifier
in contexts where this facility could possibly be in
effect, it seems safe to use it to indicate omitted
parameters in function application.

[simonmar]

This idea was discussed on the haskell-prime list and the concensus was that it should not be adopted.