Re: more flexible partial application

Hi folks John Hughes wrote:

...

On 1/23/06, Sebastian Sylvan wrote:

...

Are there any subtle reasons for why something like the following couldn't be allowed?

...

foo x y z w = ... bar x w = foo x _ _ w

Or would (f _ x) y and f _ x y maybe be different? That would fix the problem above, while introducing another. Please, no!

For what it's worth, I agree with John. In my wild and foolish youth (c1990), I implemented a programming language with this very feature. It was a kind of higher-order LOGO on the complex plane, where a function applied to a drawing transformed its coordinates. We'd do daft stuff like (200 * _ ^ 2) unitsquare What fun we had, but it was a source of top quality mystery as far as the semantics was concerned. Figuring out how to bracket stuff was total guesswork. As things stand in Haskell, parentheses do grouping, and they do sections for infix operators. These are cleanly separable, because what's in a section bracket is plainly not an expression. Extra explicit grouping of expressions is harmless. (f a) b is f a b. Giving parentheses this murky binding power interferes with their innocence. If you do want to pull a stunt like this, you need some other funny brackets which specifically indicate this binding power, and then you can do grouping inside them, to create larger linear abstractions. You could have something like (| f (_ * 3) _ |) This makes some kind of sense, provided you don't expect to be able to transform the contents of these brackets naively (| flip f _ _ |) ain't (| f _ _ |) But in my wild and foolish adulthood, I'm not sure it's worth spending a kind of bracket on. All the best Conor