Get rid of auto-currying, add syntax for currying/partial app.

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"Auto-currying" is a very cool feature for some very slick and compact code. I love being able to write (* 2) as a doubling function, for example.

However, I find that in general, auto-currying is more trouble than the entry fee it paid:

• A lot of functions aren't useful as curried.
• Many functions are better curried when flipped.
• A typo, like not including an argument when one was intended, can lead to very difficult to debug type errors.
• We work hard to de-curry as much as possible.

As such, I'd propose we break an ML/Haskell tradition and get rid of it as a default, and instead use another syntax. Some ideas follow. In the following ideas, the spirit is what I'm aiming for, i.e., whether it's _ or $ or something else is open to discussion.

Idea #1: Curry syntax

Suppose f : t -> t -> t. The syntax [f x] would represent the curried function t -> t.

Idea #2: Same as #1, but with partial application

Suppose the same f. Then the above could be written [f x _]. The other argument could be [f _ x]. Multiple arguments could be f == [f _1 _2] and flip f == [f _2 _1].