Error

An exception occurred at_exit handler
    Error trying to compile /home/nils/.rvm/gems/rbx-head/gems/antlr3-1.8.2/lib/antlr3/tree.rb (Rubinius::CompileError)

Backtrace:
     Rubinius::Compiler.compiler_error at /home/nils/.rvm/rubies/rbx-head/lib/compiler/compiler.rbc:11
            Rubinius::Compiler.compile at /home/nils/.rvm/rubies/rbx-head/lib/compiler/compiler.rbc:48
     Rubinius::CodeLoader#compile_file at kernel/delta/codeloader.rb:141
        Rubinius::CodeLoader#load_file at kernel/delta/codeloader.rb:128
          Rubinius::CodeLoader#require at kernel/common/codeloader.rb:39
          Rubinius::CodeLoader.require at kernel/common/codeloader.rb:140
  Kernel(Object)#gem_original_require (require) at kernel/common/kernel.rb:717
                Kernel(Object)#require at /home/nils/.rvm/rubies/rbx-head/lib/rubygems/custom_require.rb:31
                       main.__script__ at /home/nils/.rvm/gems/rbx-head/gems/antlr3-1.8.2/lib/antlr3/modes/ast-builder.rb:4
          Rubinius::CodeLoader.require at kernel/common/codeloader.rb:145
                         Autoload#call at kernel/common/autoload.rb:28
      ANTLR3::Main::ParserMain#present at /home/nils/.rvm/gems/rbx-head/gems/antlr3-1.8.2/lib/antlr3/main.rb:462
    ANTLR3::Main::ParserMain#recognize at /home/nils/.rvm/gems/rbx-head/gems/antlr3-1.8.2/lib/antlr3/main.rb:458
  ANTLR3::Main::Main(ANTLR3::Main::ParserMain)#execute at /home/nils/.rvm/gems/rbx-head/gems/antlr3-1.8.2/lib/antlr3/main.rb:162
                   ANTLR3::Parser.main at /home/nils/.rvm/gems/rbx-head/gems/antlr3-1.8.2/lib/antlr3/recognizers.rb:1256
    { } in AddingMachine.AddingMachine at AddingMachineParser.rb:178
             Rubinius::Loader#epilogue at kernel/loader.rb:510
                 Rubinius::Loader#main at kernel/loader.rb:599
                 Rubinius::Loader.main at kernel/loader.rb:609
                     Object#__script__ at kernel/loader.rb:621

Caused by: unbalanced stack at walk: line: 293, IP: 200: 2 != 1 (Rubinius::CompileError)

Backtrace:
  Rubinius::Generator::BasicBlock#check_stack at /home/nils/.rvm/rubies/rbx-head/lib/compiler/generator.rbc:147
  Rubinius::Generator::BasicBlock#flow_stack_size at /home/nils/.rvm/rubies/rbx-head/lib/compiler/generator.rbc:132
  Rubinius::Generator::BasicBlock#validate_stack at /home/nils/.rvm/rubies/rbx-head/lib/compiler/generator.rbc:119
            Rubinius::Generator#encode at /home/nils/.rvm/rubies/rbx-head/lib/compiler/generator.rbc:210
     { } in Rubinius::Generator#encode at /home/nils/.rvm/rubies/rbx-head/lib/compiler/generator.rbc:218
                            Array#each at kernel/bootstrap/array.rb:66
            Rubinius::Generator#encode at /home/nils/.rvm/rubies/rbx-head/lib/compiler/generator.rbc:218
     { } in Rubinius::Generator#encode at /home/nils/.rvm/rubies/rbx-head/lib/compiler/generator.rbc:218
                            Array#each at kernel/bootstrap/array.rb:66
            Rubinius::Generator#encode at /home/nils/.rvm/rubies/rbx-head/lib/compiler/generator.rbc:218
     { } in Rubinius::Generator#encode at /home/nils/.rvm/rubies/rbx-head/lib/compiler/generator.rbc:218
                            Array#each at kernel/bootstrap/array.rb:66
            Rubinius::Generator#encode at /home/nils/.rvm/rubies/rbx-head/lib/compiler/generator.rbc:218
     { } in Rubinius::Generator#encode at /home/nils/.rvm/rubies/rbx-head/lib/compiler/generator.rbc:218
                            Array#each at kernel/bootstrap/array.rb:66
            Rubinius::Generator#encode at /home/nils/.rvm/rubies/rbx-head/lib/compiler/generator.rbc:218
       Rubinius::Compiler::Encoder#run at /home/nils/.rvm/rubies/rbx-head/lib/compiler/stages.rbc:110
  Rubinius::Compiler::Stage(Rubinius::Compiler::Generator)#run_next at /home/nils/.rvm/rubies/rbx-head/lib/compiler/stages.rbc:51
     Rubinius::Compiler::Generator#run at /home/nils/.rvm/rubies/rbx-head/lib/compiler/stages.rbc:135
  Rubinius::Compiler::Stage(Rubinius::Compiler::FileParser)#run_next at /home/nils/.rvm/rubies/rbx-head/lib/compiler/stages.rbc:51
  Rubinius::Compiler::Parser(Rubinius::Compiler::FileParser)#run at /home/nils/.rvm/rubies/rbx-head/lib/compiler/stages.rbc:189
                Rubinius::Compiler#run at /home/nils/.rvm/rubies/rbx-head/lib/compiler/compiler.rbc:115
            Rubinius::Compiler.compile at /home/nils/.rvm/rubies/rbx-head/lib/compiler/compiler.rbc:44
     Rubinius::CodeLoader#compile_file at kernel/delta/codeloader.rb:141
        Rubinius::CodeLoader#load_file at kernel/delta/codeloader.rb:128
          Rubinius::CodeLoader#require at kernel/common/codeloader.rb:39
          Rubinius::CodeLoader.require at kernel/common/codeloader.rb:140
  Kernel(Object)#gem_original_require (require) at kernel/common/kernel.rb:717
                Kernel(Object)#require at /home/nils/.rvm/rubies/rbx-head/lib/rubygems/custom_require.rb:31
                       main.__script__ at /home/nils/.rvm/gems/rbx-head/gems/antlr3-1.8.2/lib/antlr3/modes/ast-builder.rb:4
          Rubinius::CodeLoader.require at kernel/common/codeloader.rb:145
                         Autoload#call at kernel/common/autoload.rb:28
      ANTLR3::Main::ParserMain#present at /home/nils/.rvm/gems/rbx-head/gems/antlr3-1.8.2/lib/antlr3/main.rb:462
    ANTLR3::Main::ParserMain#recognize at /home/nils/.rvm/gems/rbx-head/gems/antlr3-1.8.2/lib/antlr3/main.rb:458
  ANTLR3::Main::Main(ANTLR3::Main::ParserMain)#execute at /home/nils/.rvm/gems/rbx-head/gems/antlr3-1.8.2/lib/antlr3/main.rb:162
                   ANTLR3::Parser.main at /home/nils/.rvm/gems/rbx-head/gems/antlr3-1.8.2/lib/antlr3/recognizers.rb:1256
    { } in AddingMachine.AddingMachine at AddingMachineParser.rb:178
             Rubinius::Loader#epilogue at kernel/loader.rb:510
                 Rubinius::Loader#main at kernel/loader.rb:599
                 Rubinius::Loader.main at kernel/loader.rb:609
                     Object#__script__ at kernel/loader.rb:621

tree.rb

  def walk
    block_given? or return( enum_for( :walk ) )
    stack = []
    cursor = self
    while true
      begin
        yield( cursor )
        stack.push( cursor.children.dup ) unless cursor.empty?
      rescue StopIteration
        # skips adding children to prune the node
      ensure
        break if stack.empty?
        cursor = stack.last.shift
        stack.pop if stack.last.empty? # this is line 293
      end
    end
    return self
  end