kschiess/parslet — pull request #67 by frankjmattia (2012-08-12 20:06:46+00:00)
Title: Update example/calc.rb

Call to_s on operation. I'm not sure if this is the best solution. Does Parslet::Slice implement === ?

#calculate returns nil otherwise, at least on 1.9.2

#ruby -v
ruby 1.9.2p290 (2011-07-09 revision 32553) [x86_64-darwin11.1.0]