On 10 October 2010 22:32, Johannes Waldmann <waldmann@imn.htwk-leipzig.de> wrote:

Oh, and while we're at it - are there standard notations
for "forward" function composition and application?

I mean instead of h . g . f $ x
I'd sometimes prefer x ? f ? g ? h
but what are the "?"

While asking you use the same symbol for function composition, and something like inverse function application. I don't think there exists an operator ?, such that h . g . f $ x is equivalent to x ? f ? g ? h.

But you can simply define an inverse function application like the following and have a close enough alternative,

($$) :: a -> (a -> b) -> b

($$) = flip ($)

infixl 5 $$

Now the following two expression are identical, I suppose:

h . g . f $ x

x $$ f . g . h

Cheers,

Ozgur