Add a fallback for check_code_block that does not depend on implementation-private APIs

* Fixes #133

Author: eregon

lib/irb/ruby-lex.rb

@@ -222,11 +222,16 @@ def check_code_block(code)
  begin # check if parser error are available
  verbose, $VERBOSE = $VERBOSE, nil
  case RUBY_ENGINE
+ when 'ruby'
+ self.class.compile_with_errors_suppressed(code) do |inner_code, line_no|
+ RubyVM::InstructionSequence.compile(inner_code, nil, nil, line_no)
+ end
  when 'jruby'
  JRuby.compile_ir(code)
  else
- self.class.compile_with_errors_suppressed(code) do |inner_code, line_no|
- RubyVM::InstructionSequence.compile(inner_code, nil, nil, line_no)
+ catch(:valid) do
+ eval("BEGIN { throw :valid, true }\n#{code}")
+ false
  end
  end
  rescue EncodingError