From: Boris Prinz <boris.prinz@...>
Date: 2006-09-26T04:21:44+09:00
Subject: [Solution][QUIZ] Code to S-Exp (#95)

Hi,

I wouldn't use this code in a production environment, because
methods of built-in classes are redefined.

(But it also throws a lot of warnings, so...)

Best regards,
Boris



class RealityDistortionField
   OVERRIDE = [:+, :-, :*, :/, :>, :<, :>=, :<=, :==]
   CLASSES  = [Fixnum, Symbol, String]

   def self.on
     CLASSES.each do |klass|
       klass.class_eval do
         counter = 0
         OVERRIDE.each do |meth|
           # save old method:
           savemeth = "rdf_save_#{counter}".to_sym
           alias_method savemeth, meth if method_defined? meth
           counter = counter.next # since '+' is already overridden

           # override method to return an expression array:
           define_method meth do |other|
             [meth, self, other]
           end
         end
       end
     end
     # define new Object.method_missing()
     Object.class_eval do
       alias_method  :method_missing_orig, :method_missing
       define_method :method_missing do |meth, *args|
         [meth, *args]
       end
     end
   end

   # Clean up:
   def self.off
     CLASSES.each do |klass|
       klass.class_eval do
         counter = 0
         OVERRIDE.each do |meth|
           # restore original methods:
           savemeth = "rdf_save_#{counter}".to_sym
           if method_defined? savemeth
             alias_method meth, savemeth
           else
             remove_method meth
           end
           counter = counter.next
         end
       end
     end
     # restore original Object.method_missing()
     Object.class_eval do
       remove_method :method_missing
       alias_method  :method_missing, :method_missing_orig
     end
   end
end

class Object
   def sxp
     RealityDistortionField.on
     begin
       expression = yield
     ensure
       RealityDistortionField.off
     end
     expression
   end
end

require 'test/unit'

class SXPTest < Test::Unit::TestCase

   def test_quiz
     assert_equal [:max, [:count, :name]],   sxp{max(count(:name))}
     assert_equal [:count, [:+, 3, 7]],      sxp{count(3+7)}
     assert_equal [:+, 3, :symbol],          sxp{3+:symbol}
     assert_equal [:+, 3, [:count, :field]], sxp{3+count(:field)}
     assert_equal [:/, 7, :field],           sxp{7/:field}
     assert_equal [:>, :field, 5],           sxp{:field > 5}
     assert_equal 8,                         sxp{8}
     assert_equal [:==, :field1, :field2],   sxp{:field1 == :field2}
     assert_raises(TypeError)                {7/:field}
     assert_raises(NoMethodError)            {7+count(:field)}
     assert_equal 11,                        5+6
     assert_raises(NoMethodError)            {p(:field > 5)}
   end

   def test_more
     assert_equal [:+, "hello", :world], sxp{"hello" + :world}
     assert_equal [:count], sxp {count}
   end
end