Boolean expression evaluation grammar for Citrus

boolean-test.rb

require 'citrus'

Citrus.load 'boolean'

m = Boolean.parse 'false or true'
puts m.value # > true

m = Boolean.parse 'true and (!true && True) || FALSE'
puts m.value # > false

boolean.citrus

# A grammar for boolean expressions. This grammar should provide a similiar interpretation
# of boolean expressions as Ruby.
grammar Boolean

  ## Hierarchical syntax

  rule term
    oritive | factor
  end

  rule oritive
    (factor operator:(/or/i | '||') space* term) {
      capture(:factor).value || capture(:term).value
    }
  end

  rule factor
    anditive | prefix
  end

  rule anditive
    (prefix operator:(/and/i | '&&') space* factor) {
      capture(:prefix).value && capture(:factor).value
    }
  end

  rule prefix
    prefixed | primary
  end

  rule prefixed
    (operator:(/not/i | '!') space* prefix) {
      !capture(:prefix).value
    }
  end

  rule primary
    group | boolean
  end

  rule group
    (lparen term rparen) {
      capture(:term).value
    }
  end

  ## Lexical syntax

  rule boolean
    (bool_value space*) {
      to_str.rstrip.downcase.eql?('true') ? true : false
    }
  end

  rule bool_value
    /true/i | /false/i
  end

  rule lparen '(' space* end
  rule rparen ')' space* end
  rule space  [ \t\n\r]  end
end