From: "mame (Yusuke Endoh)" <mame@...>
Date: 2012-04-03T00:18:24+09:00
Subject: [ruby-core:44072] [ruby-trunk - Feature #4610][Rejected] Proc#curry behavior is inconsistent with lambdas containing default argument values


Issue #4610 has been updated by mame (Yusuke Endoh).

Status changed from Assigned to Rejected

Hello,

I don't think it is a good idea to solve the original problem by using Proc#curry.
And I like the current behavior of Proc#curry. It is simple and straightforward.


jballanc (Joshua Ballanco) wrote:
>  proc {|x, y, z, *rest| puts "#{x}, #{y}, #{z}, #{rest.join(',')}"
>  }.curry.(1).(2).(3).(4)
>  # => "1, 2, 3, 4"

It will require an extra call for invoking the proc when we want to supply no argument to the rest:

  proc {|x, y, z, *rest| puts "#{x}, #{y}, #{z}, #{rest.join(',')}"
  }.curry.(1).(2).(3).()
  # => "1, 2, 3, "


Anyway, keyword argument is implemented in trunk now.  Please give it a try first.  After that, if you still think you need anything, please reopen this ticket with clear statement about what you need.

Thanks,

-- 
Yusuke Endoh <mame@tsg.ne.jp>
----------------------------------------
Feature #4610: Proc#curry behavior is inconsistent with lambdas containing default argument values
https://bugs.ruby-lang.org/issues/4610#change-25606

Author: jballanc (Joshua Ballanco)
Status: Rejected
Priority: Normal
Assignee: mame (Yusuke Endoh)
Category: 
Target version: 


If I curry a lambda with 3 arguments, then I can call three times with one argument each time to get the desired results:

ruby-1.9.2-p180 :001 > l = ->(a, b, c) { puts "#{a}, #{b}, #{c}" }
#<Proc:0x00000100963650@(irb):1 (lambda)>
ruby-1.9.2-p180 :002 > c = l.curry
#<Proc:0x0000010095c9e0 (lambda)>
ruby-1.9.2-p180 :003 > c.('one').('two').('three')
one, two, three
nil

However, if the lambda has default values and I curry it, the entire lambda is evaluated after the first #call:


ruby-1.9.2-p180 :004 > l = ->(a = 'ichi', b = 'ni', c = 'san') { puts "#{a}, #{b}, #{c}" }
#<Proc:0x00000100877b88@(irb):4 (lambda)>
ruby-1.9.2-p180 :005 > c = l.curry
#<Proc:0x0000010086b338 (lambda)>
ruby-1.9.2-p180 :006 > c.('one').('two').('three')
one, ni, san
NoMethodError: undefined method `call' for nil:NilClass

This behavior seem very inconsistent. Ideally, if I wanted to use the default argument at a certain position in a currie proc, I would just #call with no arguments, like so:

ruby-1.9.2-p180 :007 > c.('one').().('three')
#=> Propose that this result in: "one, ni, three"



-- 
http://bugs.ruby-lang.org/