From: "T. Onoma" <transami@...>
Date: 2003-11-21T14:36:19+09:00
Subject: Re: Partial Euphoric Type Checking (now Ducked!)

quack! quack! I added duck typing capability to my euphoric type checking 
system:

  module Kernel
    def typechecking(x=nil)
      return $_tc if x == nil
      $_tc = x ? true : false
    end
  end

  class Module
    def type(tname, *resp, &check)
      define_method(tname) do |*v|
        if $_tc
          unless v.all? { |y| resp.all? { |z| y.send(:respond_to?, z) } }
            raise TypeError, "#{v}"
          end
          unless v.all? { |y| check.call(y) }
            raise TypeError, "#{v}"
          end
        end
        return *v
      end
    end
  end

Probabably could be written a little more concise. now example:

  type :big4, '>', 'to_i', 'succ' do |x|
    x > 4
  end

  def ameth(x)
    big4 x
    #---
    puts x
  end

big4 will make sure parameter responds to #> #to_i and #succ and is also 
greater than 4. 

i also have a some better ideas for sugar too:

  class TypeTest

     type big4(x)
       '>', 'to_i', 'succ'
     unless
       x > 4
     end

     def ameth(big4 x)
       puts x
     end

   end

getting better?  we may have other clauses besides 'unless' too (?) seems like 
i'm starting to converge on Sean's idea from another angle. except mine is 
dynamic runtime, but it can be turned offf globally or locally.

BUT!!!!!!!!!!! i have discovered a problem with all type systems! see next 
post....(or 2)

-t0