8 ms·

Currying is the process of turning a function that expects multiple parameters into one that, when supplied fewer parameters, returns a new function that awaits

by pettazz 12y ago

Currying is the process of turning a function that expects multiple parameters into one that, when supplied fewer parameters, returns a new function that awaits the remaining ones. I think this, along with the whole article, is the best explanation of currying I've seen on the whole damn internet.

cowbell 12y ago
It's also wrong :) http://www.uncarved.com/blog/not_currying.mrk http://www.uncarved.com/blog/not_currying.mrk Which the author freely admits: (Some will insist that what we're doing is more properly called "partial application", and that "currying" should be reserved for the cases where the resulting functions take one parameter, each resolving to a separate new function until all the required parameters have been supplied. They can please feel free to keep on insisting.)
- CrossEye 12y ago
  Yes, freely admitted. (Author here.) I feel that although the distinction can be very important, it's much less so for Javascript. And the implementation in Ramda can be used that way any time you choose: var total = reduce(add)(0); // or var sum = reduce(add)(0)(numbers) works just as well in Ramda as var total = reduce(add, 0); // or var sum = reduce(add, 0, numbers) So, as I said, feel free to keep on insisting. :-)
  - cowbell 12y ago
    http://vimeo.com/96639840 http://vimeo.com/96639840 Start at 26mins. You don't have flip. You lose control over partial application. It isn't curry. You're right. It is an important distinction :)
    - comex 12y ago
      This implementation of multi-argument partial application does not in any say prevent implementation of flip. It's just syntax sugar.
    - CrossEye 12y ago
      I finally got a chance to watch that video, and it looks as though what you're worried about is `flip`. Ramda for one already includes a version that works much like Haskell's. I don't know if this satisfies your objection, though.
      - tel 12y ago
        As I stated above... flip is well defined so long as your arguments are positional.
- tel 12y ago
  As long as you have ordered parameters, I'm not sure this is such a big issue. First, tuples are (morally, i.e. up to non-termination) associative in most reasonable languages, so the product/exponential adjunction can be shifted around however you like -- all morally identical a -> b -> c -> d a -> (b -> c -> d) a -> (b -> (c -> d)) (a, b) -> c -> d (a, b, c) -> d ((a, b), c) -> d (a, (b, c)) -> d However, so long as you have parameter order (we're not allowed to commute our tuples, just reassociate nested tuples like ((a, b), c) <-> (a, (b, c)) and so on) then flip still morally works flip (someFn :: (a, b, c) -> d) :: (b, a, c) -> d :: (b, a) -> c -> d :: b -> a -> (c -> d) The same story holds for partial evaluation. Of course, there have to be far more edge cases to handle all this tuple twiddling. --- Really, I think it's pretty meaningful to blur the distinction between "curry (once)" and "curry repeatedly along with tuple reassociation". The later forms an equivalence class of function types which all have the same application behavior.
  - tel 12y ago
    Also to explain that strange "adjunction" comment, currying results from the notion that the things of type (a, b) -> c are exactly equivalent to the things of type a -> (b -> c) An adjunction (F, G) occurs when the things of type (F a -> c) are equivalent to things of type (a -> G c), so if we pick F x = (x, b) and G x = (b -> x) then we see that currying is an adjunction between (,b) and (b ->).
    - evincarofautumn 12y ago
      One intuition for this is that (a, b) is the product type (a × b) and the function arrow (a → b) corresponds to exponentiation (b^a), so you get the isomorphism for free from the identity c^(a × b) = (c^b)^a.

by pettazz 12y ago

cowbell 12y ago

It's also wrong :) http://www.uncarved.com/blog/not_currying.mrk http://www.uncarved.com/blog/not_currying.mrk Which the author freely admits: (Some will insist that what we're doing is more properly called "partial application", and that "currying" should be reserved for the cases where the resulting functions take one parameter, each resolving to a separate new function until all the required parameters have been supplied. They can please feel free to keep on insisting.)

CrossEye 12y ago
Yes, freely admitted. (Author here.) I feel that although the distinction can be very important, it's much less so for Javascript. And the implementation in Ramda can be used that way any time you choose: var total = reduce(add)(0); // or var sum = reduce(add)(0)(numbers) works just as well in Ramda as var total = reduce(add, 0); // or var sum = reduce(add, 0, numbers) So, as I said, feel free to keep on insisting. :-)
- cowbell 12y ago
  http://vimeo.com/96639840 http://vimeo.com/96639840 Start at 26mins. You don't have flip. You lose control over partial application. It isn't curry. You're right. It is an important distinction :)
  - comex 12y ago
    This implementation of multi-argument partial application does not in any say prevent implementation of flip. It's just syntax sugar.
  - CrossEye 12y ago
    I finally got a chance to watch that video, and it looks as though what you're worried about is `flip`. Ramda for one already includes a version that works much like Haskell's. I don't know if this satisfies your objection, though.
    - tel 12y ago
      As I stated above... flip is well defined so long as your arguments are positional.
tel 12y ago
As long as you have ordered parameters, I'm not sure this is such a big issue. First, tuples are (morally, i.e. up to non-termination) associative in most reasonable languages, so the product/exponential adjunction can be shifted around however you like -- all morally identical a -> b -> c -> d a -> (b -> c -> d) a -> (b -> (c -> d)) (a, b) -> c -> d (a, b, c) -> d ((a, b), c) -> d (a, (b, c)) -> d However, so long as you have parameter order (we're not allowed to commute our tuples, just reassociate nested tuples like ((a, b), c) <-> (a, (b, c)) and so on) then flip still morally works flip (someFn :: (a, b, c) -> d) :: (b, a, c) -> d :: (b, a) -> c -> d :: b -> a -> (c -> d) The same story holds for partial evaluation. Of course, there have to be far more edge cases to handle all this tuple twiddling. --- Really, I think it's pretty meaningful to blur the distinction between "curry (once)" and "curry repeatedly along with tuple reassociation". The later forms an equivalence class of function types which all have the same application behavior.
- tel 12y ago
  Also to explain that strange "adjunction" comment, currying results from the notion that the things of type (a, b) -> c are exactly equivalent to the things of type a -> (b -> c) An adjunction (F, G) occurs when the things of type (F a -> c) are equivalent to things of type (a -> G c), so if we pick F x = (x, b) and G x = (b -> x) then we see that currying is an adjunction between (,b) and (b ->).
  - evincarofautumn 12y ago
    One intuition for this is that (a, b) is the product type (a × b) and the function arrow (a → b) corresponds to exponentiation (b^a), so you get the isomorphism for free from the identity c^(a × b) = (c^b)^a.