Re: more flexible partial application

On 1/26/06, Aaron Denney wrote:

On 2006-01-26, Dinko Tenev wrote:

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On 1/26/06, Conor McBride wrote: [...]

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We'd do daft stuff like

(200 * _ ^ 2) unitsquare

Yes, I played with a concept like that at one point, and came to the conclusion that it was better done with lambdas. I am all specifically about function application, not arbitrary expressions.

Arbitrary expressions are just function application.

...arbitrarily deeply nested. I meant looking at a single level of function application, with all the consequences for how high up the tree the underscore may "escape" as a lambda. You're probably going to tell me that f x y z represents 3 different levels, but many folks would see this as little more than a cute way of writing f(x, y, z), and they'll have a point, given how the concept of "partial" application is bandied every so often. It is quite reasonable to identify a minimal enclosing application, with all visible arguments consumed up to the innermost enclosing pair of parentheses. Sure, it's not a very elegant concept, but neither is the current mechanism for operator sections (which does exactly the same.) The only implication will be that you won't be able to use sections *and* emphasize the order of application at the same time, and I am yet to hear from anyone who prefer (((f x) y) z) to (f x y z) in their code. BTW, it just occurred to me that if this section syntax is extended to operators as well, it would cure the rather embarrassing case of the "-" operator :)

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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) _ |)

We already have lambdas for this, and they're shorter, clearer, and more powerful.

The same hold (except for shorter) for this whole extension, and I don't know that "shorter" holds here.

I missed an underscore, so you have your point about "shorter." About the whole extension, (f x _ z) is arguably clearer than \y -> f x y z, and is also really unobtrusive syntactic sugar, very much unlike a new kind of brackets.

-- Aaron Denney -><-

Cheers, Dinko