From: jweirich@...
Date: 2001-02-17T12:59:46+09:00
Subject: [ruby-talk:11007] Generators (was: RCR Summary 02/16/01 -suspend)


    Hugh> Icon has the suspend command which allows a function to
    Hugh> produce a result in the way that return does, but it
    Hugh> suspends execution so that if the function is called again
    Hugh> in the same context execution can continue from where the
    Hugh> suspend left off. It could be considered to be an inside-out
    Hugh> yield. This is used to create generators rather than
    Hugh> iterators. It is achieved by leaving the state of the
    Hugh> function on the stack.

How about this ...

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require 'generator'

class FibGenerator < Generator
  def generating_loop
    generate(1)
    a, b = 1, 1
    loop do
      generate(b)
      a, b = b, a+b
    end
  end
end

fib = FibGenerator.new

puts fib.next # => 1
puts fib.next # => 1
puts fib.next # => 2
puts fib.next # => 3
puts fib.next # => 5
puts fib.next # => 8
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Its done with mirrors (and continuations) ...

-- File: generator.rb ------------------------------------------------
#!/usr/bin/env ruby
# -*- ruby -*-

class Generator
  def initialize
    do_generation
  end

  def next
    callcc { |here|
      @main_context = here;
      @generator_context.call
    }
  end

  private

  def do_generation
    callcc { |context|
      @generator_context = context;
      return
    }
    generating_loop
  end
  
  def generate(value)
    callcc { |context|
      @generator_context = context;
      @main_context.call(value)
    }
  end
end
----------------------------------------------------------------------