From: Yusuke Endoh <mame@...>
Date: 2011-04-26T02:28:19+09:00
Subject: [ruby-core:35885] [Ruby 1.9 - Bug #4610] Proc#curry behavior is inconsistent with lambdas containing default argument values


Issue #4610 has been updated by Yusuke Endoh.

Target version set to 2.0

Hello,

2011/4/25 Joshua Ballanco <jballanc@gmail.com>:
> This behavior seem very inconsistent.

Indeed, it is arguable how Proc#curry should handle optional parameters,
but I don't think it is inconsistent.  In either case, a curried Proc
fires its execution as soon as required arguments are given.

At least, this is intended, not a bug.
So I'm moving this ticket to 2.0 feature request tracker.


> 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"

It is interesting, but incompatible with the current behavior.
And I can think that it will be even inconsistent:

  c.('one', 'two').(              'three') #=> one, two, three
  c.('one')       .(       'two', 'three') #=> one, two, three
  c.()            .('one', 'two', 'three') #=> wrong number of arguments

-- 
Yusuke Endoh <mame@tsg.ne.jp>
----------------------------------------
Bug #4610: Proc#curry behavior is inconsistent with lambdas containing default argument values
http://redmine.ruby-lang.org/issues/4610

Author: Joshua Ballanco
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 2.0
ruby -v: 1.9.2p180


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://redmine.ruby-lang.org