Matching plural words in Treetop

Question

Is there a way to programmatically match plural words using Treetop. The Linguistics gem will pluralize a word, but how can that be inserted back into the parser.

Here's an example of what I'm trying to do:

#!/usr/bin/env ruby
require 'treetop'
require 'linguistics'
include Linguistics::EN
Treetop.load_from_string DATA.read

parser = RecipeParser.new

p parser.parse('cans')

__END__
grammar Recipe
   rule units
      unit &{|s| plural(s[0].text_value) }  
   end
   rule unit
      'can'
   end
end

Answer 1

In general, the linguistics gem can't pluralize arbitrary Treetop rule definitions—they're not strings.

Using semantic predicates your recipe.treetop file could define all your valid singular unit strings in an array, pluralize them, and then create a rule that compares the token in question to each of those pluralized units:

require "linguistics"

grammar Recipe
  rule units
    [a-zA-Z\-]+ &{ |u|
      Linguistics.use(:en)
      singular_units = [ "can" ]

      singular_units.
        map(&:en).
        map(&:plural).
        include?(u[0].text_value)
    }
  end
end