Syntax error when parsing 1.9 syntax for lambda with empty parentheses

[gregspurrier]

If the argument list for a lambda expression using Ruby 1.9's arrow syntax is a set of empty parentheses, JRuby throws a syntax error:

irb(main):001:0> RUBY_ENGINE
=> "jruby"
irb(main):002:0> JRUBY_VERSION
=> "1.7.19"
irb(main):003:0> -> () {}
SyntaxError: (irb):3: syntax error, unexpected tLPAREN_ARG
-> () {}
   ^
        from org/jruby/RubyKernel.java:1107:in `eval'
        from org/jruby/RubyKernel.java:1507:in `loop'
        from org/jruby/RubyKernel.java:1270:in `catch'
        from org/jruby/RubyKernel.java:1270:in `catch'
        from /home/greg/.rbenv/versions/jruby-1.7.19/bin/irb:13:in `(root)'

Contrast this with MRI, which accepts this syntax:

irb(main):001:0> RUBY_ENGINE
=> "ruby"
irb(main):002:0> RUBY_VERSION
=> "2.2.1"
irb(main):003:0> -> () {}
=> #<Proc:0x007f03f6ab8988@(irb):3 (lambda)>

[enebo]

This was apparently a change in grammar introduced in Ruby 2.0 and Ruby 1.9.3 seems to behave the same way for me:

mri19 -ve '-> () {}'
ruby 1.9.3p551 (2014-11-13 revision 48407) [x86_64-darwin13.4.0]
-e:1: syntax error, unexpected tLPAREN_ARG, expecting keyword_do_LAMBDA or tLAMBEG
-> () {}
    ^

This is working ok in JRuby 9k (which is 2.2.1) so I am resolving this.