From: Ross Bamford <rossrt@...>
Date: 2006-02-03T00:03:40+09:00
Subject: Re: [SUMMARY] Port a Library (#64)

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On Thu, 2006-02-02 at 22:37 +0900, Ruby Quiz wrote:
> The library already supports a bunch of "spices", like HOLE above, but
> you can also add your own:
> 
> 	# Lazy Evaluation meets Currying...
> 	class LazySpice < Curry::SpiceArg
> 	  def initialize( &promise )
> 	    super("LAZYSPICE")
> 	    
> 	    @promise = promise
> 	  end
> 	  
> 	  def spice_arg( args )  # called to provide the missing argument
> 	    [@promise.call]
> 	  end
> 	end
> 	
> 	logger = lambda do |time, message|
> 	  puts "[#{time.strftime('%I:%M:%S %p %m/%d/%y')}] #{message}"
> 	end
> 	
> 	log_now = logger.curry(LazySpice.new { Time.now })
> 	
> 	log_now["First Message."]   # => [12:47:53 PM 02/01/06] First Message.
> 	sleep 3
> 	log_now["Second Message."]  # => [12:47:56 PM 02/01/06] Second Message.
> 
> Notice how the LazySpice isn't evaluated until the time of the call.  That lazy
> execution makes sure our message is stamped with the time it was actually
> logged.

This is very cool, thanks for the great write-up. However, there is a
small bug (in curry.rb, not this code) that can cause problems with
this, e.g:

	a = [1,3,5]
	b = [2,4,6]

	l = lambda do |ary,aa,ba| 
	  ary +	[aa,ba] 
	end.curry(Curry::HOLE,Curry::HOLE,TestSpice.new { b.shift })

	l.call
	# => [1,nil,3,nil,5,nil]    (expected: 1,2,3,4,5,6)

This only shows up when special spices are at the end of the argument
list, and happens because there are no args_remain left by the time
they're seen, and I took a short-cut in the implementation. The attached
patch (against the documented version from
http://roscopeco.co.uk/code/ruby-quiz-entries/64/curry.rb) fixes things.
There maybe a slight impact on performance, though (if that matters).

I'm considering maybe packaging Ruby Murray up as a gem and releasing it
on RubyForge. I'll add James' LazySpice, and would like any suggestions
others may have (esp if anyone has something we could legitimately call
"SportySpice" ;D) 

Thanks again for the quiz. Cool entries everyone :)

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

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--- curry-orig.rb       2006-02-02 14:45:23.000000000 +0000
+++ curry.rb    2006-02-02 14:40:39.000000000 +0000
@@ -7,7 +7,14 @@
 #
 # You can download Ruby Murray (with documentation and explanatory
 # comments) from http://roscopeco.co.uk/ruby-quiz-entries/64/curry.rb
-
+#
+# == Changelog
+#
+# 0.1.0 - 2005/01/27 - First version
+# 0.1.2 - 2005/02/02 - Changed call_spice behaviour when processing
+#                      leftover SpiceArgs, arg is now called with
+#                      no remaining args.
+#
 require 'singleton'

 # *Ruby* *Murray* is a Ruby port of Perl's Sub::Curry library that allows
@@ -235,11 +242,11 @@
   # Merges, then resolves all special spices
   def call_spice(args)
     sp = merge_spice(args)
-    sp.map do |a|
+    sp.inject([]) do |ary, a|
       if a.is_a? SpiceArg
-        nil
+        ary + a.spice_arg([])
       else
-        a
+        ary << a
       end
     end
   end
@@ -442,6 +449,24 @@
       s = Sub::Curry.new(s.method(:+), "ing")
       assert_equal "string", s.call
     end
+
+    class TestSpice < Curry::SpiceArg
+      def initialize(&blk)
+        @blk = blk
+      end
+      def spice_arg(args_remain)
+        [@blk.call]
+      end
+    end
+
+    def test_spice_at_end_regression
+      a = [1,3,5]
+      b = [2,4,6]
+      l = lambda { |ary,aa,ba| ary + [aa,ba] }.curry(Curry::HOLE,Curry::HOLE,TestSpice.new { b.shift })
+
+      # bug behaviour: assert_equal [1,nil,3,nil,5,nil]
+      assert_equal [1,2,3,4,5,6], a.inject([], &l)
+    end
   end

   if ARGV.member?('--doc') || !File.exist?('doc')


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