From: Ross Bamford <rossrt@...>
Date: 2006-01-30T00:13:54+09:00
Subject: Re: [QUIZ][SOLUTION] Port a Library (#64)

(By my calculations it's gone 48 hours now? Hope so, anyway...) 

I did "Ruby Murray" - a port of Johan Lodin's Sub::Curry from Perl. It's
not so useful in Ruby I guess but it's fun and pretty flexible. Below is
the uncommented version, but since I can't sleep when I have
undocumented code I did Rdoc it and make the commented version available
at http://roscopeco.co.uk/code/ruby-quiz-entries/64/ .

There's also a translation of the Sub::Curry cookbook I used to drive
development a bit. The original Sub::Curry can be found at
http://search.cpan.org/~lodin/Sub-Curry-0.8/lib/Sub/Curry.pm and the
cookbook is at
http://search.cpan.org/~lodin/Sub-Curry-0.8/lib/Sub/Curry/Cookbook.pod .

Ruby Murray is about a hundred lines for the main Curry class, another
forty or so for convenience methods and the like, and about 70 lines of
tests. It could be smaller but I like (reasonably) readable code and the
TDD makes it more verbose I guess...

Here's a couple of quick examples. See the cookbook and tests (either
below or in the Rdoc linked above if formatting is broken) for more.

Just curry a method:

	c = "string".method(:slice).curry(Curry::HOLE,2)
	c.call(0)
	# => "st"
	c.call(2)
	# => "ri"

Swallow arguments:

	curry = lambda { |*args| args }.curry(1,Curry::ANTISPICE,3)
	curry.call(2,5)
	# => [1,3,5]

Do some mad curry to curry stuff:

	curry = [10,20,30].method(:inject).curry(Curry::HOLE)
	curry.call(0) { |s,i| s + i }
	# => 60

	mult_sum = lambda do |sum, i, mult| 
	  sum + (i * mult) 
	end.curry(Curry::BLACKHOLE, Curry::HOLE)

	double_sum = mult_sum.new(Curry::BLACKHOLE, Curry::WHITEHOLE, 2)
	triple_sum = mult_sum.new(Curry::BLACKHOLE, Curry::WHITEHOLE, 3)

	curry.call(0, &double_sum)
	# => 120

	curry.call(0, &triple_sum)
	# => 180	

Obviously it's completely different from the Perl original under the
hood but I tried to make it familiar enough while making good use of
Ruby.

There's a few other ideas I'd like to have tried but I didn't want to
get too far into it ;). One advantage this version has over Perl's is
that it's easy to make custom Spice argument types (HOLE, BLACKHOLE,
etc) so maybe there's some scope for hacking around in there...

=====[CURRY.RB]=====
require 'singleton'

class Curry
  WHITEHOLE = Object.new
  ANTIHOLE = Object.new
  def WHITEHOLE.inspect #:nodoc:
    "<WHITEHOLE>"
  end 
  def ANTIHOLE.inspect #:nodoc:
    "<ANTIHOLE>"
  end
  
  class SpiceArg
    def initialize(name)
      @name = name
    end
    def spice_arg(args_remain)
      raise NoMethodError, "Abstract method"
    end
    def inspect
      "<#{@name}>"
    end
  end

  class HoleArg < SpiceArg #:nodoc: all
    include Singleton
    def initialize; super("HOLE"); end
    def spice_arg(args_remain)
      a = args_remain.shift
      if a == ANTIHOLE
        []
      else
        [a]
      end
    end
  end
  
  class BlackHoleArg < SpiceArg #:nodoc: all
    include Singleton
    def initialize; super("BLACKHOLE"); end
    def spice_arg(args_remain)
      if idx = args_remain.index(WHITEHOLE)        
        args_remain.slice!(0..idx)[0..-2]
      else
        args_remain.slice!(0..args_remain.length)
      end
    end
  end

  class AntiSpiceArg < SpiceArg #:nodoc: all
    include Singleton
    def initialize; super("ANTISPICE"); end
    def spice_arg(args_remain)
      args_remain.shift
      []
    end
  end

  HOLE = HoleArg.instance
  BLACKHOLE = BlackHoleArg.instance
  ANTISPICE = AntiSpiceArg.instance
 
  attr_reader :spice
  attr_reader :uncurried

  def initialize(*spice, &block)
    block = block || (spice.shift if spice.first.respond_to?(:call))
    raise ArgumentError, "No block supplied" unless block
    @spice, @uncurried = spice, block
  end

  def call(*args, &blk)
    @uncurried.call(*call_spice(args), &blk)
  end

  # This would be an alias, but it's documented along with call and
  # I couldn't :nodoc: an alias - how do we do that ?
  def [](*args) # :nodoc:
    call(*args)
  end

  def new(*spice)
    Curry.new(*merge_spice(spice), &@uncurried)
  end

  def to_proc
    @extern_proc ||= method(:call).to_proc
  end 
  
  private 

  def merge_spice(spice)
    largs = spice.dup
    
    res = @spice.inject([]) do |res, sparg|
      if sparg.is_a?(SpiceArg) && !largs.empty?
        res + sparg.spice_arg(largs)
      else
        res << sparg
      end
    end
   
    res + largs
  end

  def call_spice(args)
    sp = merge_spice(args)
    sp.map do |a| 
      if a.is_a? SpiceArg
        nil
      else
        a
      end
    end
  end
end

# Undocumented alias for Perl familiarity
module Sub #:nodoc: all
  Curry = ::Curry
end

module Curriable
  def curry(*spice)
    Curry.new(self, *spice)
  end
end

unless defined? NO_CORE_CURRY
  NO_CORE_CURRY = (ENV['NO_CORE_CURRY'] || $SAFE > 3)
end

unless NO_CORE_CURRY
  class Proc
    include Curriable
  end

  class Method
    include Curriable
  end
end

if $0 == __FILE__ || (TEST_CURRY if defined? TEST_CURRY)
  require 'test/unit'

  class TestCurry < Test::Unit::TestCase
    def test_fixed_args
      curry = Curry.new(1,2,3) { |a,b,c| [a,b,c] }
      assert_equal [1,2,3], curry.call
    end

    def test_fixed_array_args
      curry = Curry.new([1],[2,3]) { |*args| args }
      assert_equal [[1],[2,3]], curry.call
    end

    def test_hole
      curry = Curry.new(1,Curry::HOLE,3) { |a,b,c| [a,b,c] }
      assert_equal [1,nil,3], curry.call
      assert_equal [1,2,3], curry.call(2)

      curry = Curry.new(1,Curry::HOLE,3,Curry::HOLE) { |*args| args }
      assert_equal [1,2,3,4], curry.call(2,4)
      assert_equal [1,2,3,4,5,6], curry.call(2,4,5,6)
      assert_equal [1,[2,'two'],3,[4,0],[[14]]], 
                   curry.call([2,'two'],[4,0],[[14]])
      
    end

    def test_antihole
      curry = Curry.new(1,Curry::HOLE,3) { |*args| args }
      assert_equal [1,3], curry.call(Curry::ANTIHOLE)

      curry = Curry.new(1,Curry::HOLE,3,Curry::HOLE,4) { |*args| args }
      assert_equal [1,2,3,4,5], curry.call(2,Curry::ANTIHOLE,5)
    end

    def test_antispice
      curry = Curry.new(1,Curry::ANTISPICE,3,Curry::HOLE,4) { |*args|
args }
      assert_equal [1,3,4,5], curry.call(2,Curry::ANTIHOLE,5)
    end

    def test_black_hole
      curry = Curry.new(1,Curry::BLACKHOLE) { |*args| args }
      assert_equal [1,2,3], curry.call(2,3)

      curry = Curry.new(1,Curry::BLACKHOLE,3,4) { |*args| args }
      assert_equal [1,2,10,3,4], curry.call(2,10)
    end

    def test_white_hole
      curry = Curry.new(1,Curry::BLACKHOLE,3,Curry::HOLE,5) { |*args|
args }
      assert_equal [1,2,3,7,5,8,9], curry.call(2,Curry::WHITEHOLE,7,8,9)
      assert_equal [1,10,20,3,nil,5], curry.call(10,20,Curry::WHITEHOLE)
      assert_equal [1,10,20,25,3,4,5],
curry.call(10,20,25,Curry::WHITEHOLE,4)

      curry =
Curry.new(1,Curry::BLACKHOLE,6,Curry::HOLE,3,4,Curry::BLACKHOLE,5) { |
*args| args }
      assert_equal [1,10,20,25,6,40,3,4,50,60,5],
curry.call(10,20,25,Curry::WHITEHOLE,40,50,60)
    end

    def test_curry_from_curry
      curry =
Curry.new(1,Curry::BLACKHOLE,6,Curry::HOLE,3,4,Curry::BLACKHOLE,5) { |
*args| args }
      curry = curry.new(Curry::HOLE,Curry::WHITEHOLE,8,9,10)
      assert_equal [1,Curry::HOLE,6,8,3,4,9,10,5], curry.spice

      curry = curry.new(Curry::HOLE, 4, Curry::BLACKHOLE)
      assert_equal [1,Curry::HOLE,6,8,3,4,9,10,5,4,Curry::BLACKHOLE],
curry.spice

      curry = curry.new(Curry::ANTIHOLE)
      assert_equal [1,6,8,3,4,9,10,5,4,Curry::BLACKHOLE], curry.spice

      curry = curry.new(3,Curry::BLACKHOLE,Curry::WHITEHOLE,0)
      assert_equal [1,6,8,3,4,9,10,5,4,3,Curry::BLACKHOLE,0],
curry.spice
      assert_equal [1,6,8,3,4,9,10,5,4,3,2,1,0], curry.call(2,1)
    end

    def test_cant_block_to_curried_block
      a = Curry.new(1,2) { |*args| args }

      assert_equal [1,2,3], a.call(3) { |b| }
    end

    def test_curry_proc
      a = [1,2,3,4,5]
      c = Curry.new(*a) { |*args| args * 2 }
      assert_equal [1,2,3,4,5,1,2,3,4,5], c.call

      if NO_CORE_CURRY
        warn "Skipping Proc extension test"
      else
        c = lambda { |*args| args * 2 }.curry(*a)
        assert_equal [1,2,3,4,5,1,2,3,4,5], c.call
      end
    end

    def test_curry_method
      a = [1,2,3,4,5]
      injsum = Curry.new(a.method(:inject),0)
      assert_equal 15, injsum.call { |s,i| s + i }

      if NO_CORE_CURRY
        warn "Skipping Method extension test"
      else
        injsum = a.method(:inject).curry(0)
        assert_equal 15, injsum.call { |s,i| s + i }
      end
    end

    def test_curry_to_proc
      curry = Curry.new(Curry::HOLE, Curry::HOLE, 'thou') { |ary,i,msg|
ary << "#{i} #{msg}" }
      assert_equal ["1 thou", "2 thou", "3 thou"],
[1,2,3].inject([],&curry) 
    end

    def test_alt_bits
      curry = Curry.new(Curry::BLACKHOLE, 'too', 'true') { |one, two,
*rest| [one, two, rest] }
      assert_equal [1,2,['too','true']], curry[1,2]
    end

    def test_perlish
      s = "str"
      s = Sub::Curry.new(s.method(:+), "ing") 
      assert_equal "string", s.call
    end
  end

  if ARGV.member?('--doc') || !File.exist?('doc')
    ARGV.reject! { |a| a == '--doc' }
    system("rdoc #{__FILE__} #{'currybook.rdoc' if
File.exists?('currybook.rdoc')} --main Curry")
  end
end  

__END__

-- 
Ross Bamford - rosco@roscopeco.REMOVE.co.uk