rbx-instance_eval-bug.rb

# In file scope.rb

# Expected output:
# BEFORE: 0, AFTER: 0
# BEFORE: 1, AFTER: 1
# BEFORE: 2, AFTER: 2
# BEFORE: 3, AFTER: 3
# BEFORE: 4, AFTER: 4
# BEFORE: 5, AFTER: 5
# BEFORE: 6, AFTER: 6
# 720

# Actual output:
# BEFORE: 0, AFTER: 0
# BEFORE: 0, AFTER: 0, AFTER: 0
# BEFORE: 0, AFTER: 0, AFTER: 0, AFTER: 0
# BEFORE: 0, AFTER: 0, AFTER: 0, AFTER: 0, AFTER: 0
# BEFORE: 0, AFTER: 0, AFTER: 0, AFTER: 0, AFTER: 0, AFTER: 0
# BEFORE: 0, AFTER: 0, AFTER: 0, AFTER: 0, AFTER: 0, AFTER: 0, AFTER: 0
# BEFORE: 0, AFTER: 0, AFTER: 0, AFTER: 0, AFTER: 0, AFTER: 0, AFTER: 0, AFTER: 0
# 720

class Scope
  def initialize
    @symbols = {}
    
    # This works:
    # define('fact') do |x|
    #   str = "BEFORE: #{x}"
    #   result = x == 0 ? 1 : x * self.call('fact', x-1)
    #   str << ", AFTER: #{x}"
    #   puts str
    #   result
    # end
    
    # This does not:
    path = File.join(File.dirname(__FILE__), 'fact.rb')
    instance_eval(File.read(path))
  end
  
  def define(name, &body)
    @symbols[name] = Function.new(body)
  end
  
  def call(name, *args)
    @symbols[name].call(*args)
  end
end

class Function
  def initialize(body)
    @body = body
  end
  
  def call(*args)
    @body.call(*args)
  end
end


scope = Scope.new
puts scope.call('fact', 6)


# In file fact.rb

define('fact') do |x|
  str = "BEFORE: #{x}"
  result = x == 0 ? 1 : x * self.call('fact', x-1)
  str << ", AFTER: #{x}"
  puts str
  result
end