Feature #6817: Partial application

• Status: Assigned
• Assignee: matz (Yukihiro Matsumoto)
• Target version: -

[citizen428 (Michael Kohl)]

I know that what I propose here is a significant change to Ruby, but it's part of my ongoing quest to get some more functional programming features into Ruby (see also #4539 and #6373).

I was wondering if it would make sense to maybe introduce partial application to Ruby? So that instead of

(1..3).map { |i| i + 2 }

or the somewhat unwieldy

(1..3).map(&2.method(:+))

one could just write

(1..3).map(&2.+)

which I think has a quite rubyish feel to it. I have a POC implementation in Ruby (I tried it with various Fixnum methods) over at my blog, but that was just a quick hack and obviously I don't want to monkey-patch every method with arity 1, but it was a nice way of exploring possible syntax.

[shyouhei (Shyouhei Urabe)]

• Description updated (diff)

[yhara (Yutaka HARA)]

• Target version changed from 2.0.0 to 2.6

[ko1 (Koichi Sasada)]

• Assignee set to matz (Yukihiro Matsumoto)

This ticket is related to [ruby-core:52797] [ruby-trunk - Feature #7939]?
(definitely no?)

Basically, I like this proposal.
But I'm not sure this notation can be acceptable.

FYI: Scheme has similar, but more flexible proposal:
http://srfi.schemers.org/srfi-26/srfi-26.html

(cut cons (+ a 1) <>) is the same as (lambda (x2) (cons (+ a 1) x2))
(cut list 1 <> 3 <> 5) is the same as (lambda (x2 x4) (list 1 x2 3 x4 5))
(cut list) is the same as (lambda () (list))
(cut list 1 <> 3 <...>) is the same as (lambda (x2 . xs) (apply list 1 x2 3 xs))
(cut <> a b) is the same as (lambda (f) (f a b))

Of course, it is not ruby's way. This is only sample of the other language.

[citizen428 (Michael Kohl)]

Koichi Sasada wrote:

Basically, I like this proposal.
But I'm not sure this notation can be acceptable.

In that case, how about making Symbol#to_proc accept additional arguments?

(1..3).map(:+, 2) 

The syntax would be very straightforward, but it doesn't go well with the current implementation of Symbol#to_proc's proc cache. Also this does go away a bit from the original point of partial application, though tbh this sort of scenario is what I mostly had in mind anyway.

[nobu (Nobuyoshi Nakada)]

• Description updated (diff)

Michael Kohl wrote:

In that case, how about making Symbol#to_proc accept additional arguments?

(1..3).map(:+, 2) 

It doesn't relate to Symbol#to_proc.

[k0kubun (Takashi Kokubun)]

• Related to Feature #7939: Alternative curry function creation added

[k0kubun (Takashi Kokubun)]

• Related to Feature #13765: Add Proc#bind added

[naruse (Yui NARUSE)]

• Target version deleted (2.6)

[hsbt (Hiroshi SHIBATA)]

• Status changed from Open to Assigned