Proposed: _.call2, _.mapArgs, and _.mapArgsWith

[raganwald]

_.call2 is a utility-function that subsumes calling, partial application, and currying. You can write:

_.call2(fun, 1, 2)
_.call2(fun, 1)(2)
_.call2(fun)(1, 2)
_.call2(fun)(1)(2)

This facilitates a lot of other combinator writing.

_.mapArgs takes a function and returns a version that performs a map on its arguments. Example:

function echo () {
  return [].slice.call(arguments, 0);
}
function square (n) { return n * n; }
_mapArgs(echo, square)(1, 2, 3) //=> [1, 4, 9]

_.mapArgsWith is the same thing, with its arguments flipped to facilitate partial application of the mapper as a decorator.

These functions are integral to a post I'm writing about underscore-contrib :-)

[fogus]

One (strong) way that I diverge philosophically from _ is in my view on "magic" arguments. With that said, call2 makes me feel a little queasy. I'd prefer different names for different tasks. Explicit is better than implicit?

Looking over your mappy function one thing that jumped out at me was that baseMapArgs is a variant of _.walk.map, now available in _.contrib. :-)

[raganwald]

With call2, I'm trying to emulate the semantics of languages where everything is curried by default, and writing foo(bar, blitz) is syntactic sugar for writing foo(bar)(blitz). When you then consider call2(foo, bar, blitz), it follows that since call2 itself is curried by default, you get the behaviour written above.

However, I can see the argument that _.contrib is a different world, so I will make it rain accordingly.

[raganwald]

I've reviewed _.walk.map, and I'm not sure how to use _walk.map on it, except possibly to replace __map.call on arguments. Could you elaborate?