screw_you_jpw.rb

def myfunc(prog = "")
  mystr = "hi there"
  eval(prog)
  mystr.scream
end

puts 'first'
begin
  myfunc
rescue => e
  puts "got error #{e}"
end

puts '================'
puts 'second'
begin
  myfunc('class String; def scream; $stdout.puts self.upcase; end; end;')
rescue => e
  puts "got error #{e}"
end

class Screamer
  def scream
    puts 'AAAAAAH'
  end
end

puts '================'
puts 'third'
begin
  myfunc('mystr = Screamer.new')
rescue => e
  puts "got error #{e}"
end

=begin
first
got error undefined method `scream' for "hi there":String
================
second
HI THERE
================
third
AAAAAAH
=end