From: Joel VanderWerf <vjoel@...>
Date: 2006-01-15T05:00:04+09:00
Subject: comparison operations in case statements


This looks kind of cute, as a way to mix class-matching tests with
comparison operator tests in case statements. Too bad it's not really
practical (the commented out caching may help a bit, but may also use
too much memory):

class Comparator < Proc
  def ===(val)
    call val
  end

  def &(other)
    compare do |val|
      self[val] and other[val]
    end
  end
end

def compare
  Comparator.new
end

class Numeric
  #@comparator_lt = {}
  def self.<(x)
    #@comparator_lt[x] ||=
    compare do |val|
      self === val and val < x
    end
  end

  #@comparator_gt = {}
  def self.>(x)
    #@comparator_gt[x] ||=
    compare do |val|
      self === val and val > x
    end
  end
end


raise unless (Numeric < 6) === 3
raise if (Integer < 6) === 2.3
raise if (Integer < 6) === "foo"

case 3
when (Numeric < 6) & (Numeric > 5); raise
when (Numeric < 0) & (Numeric > -10); raise
when (Numeric < 6) & (Numeric > 2)
else raise
end

-- 
      vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407