Convert JSGF grammars to Alexa examples using Ruby

jsgf_alexa.rb

require 'jsgf'

module JSGF
    class Grammar
        # Convert a {Grammar} into a set of sample utterances for Alexa
        # @option slots [Array]         The rule names that should be used as slot names
        # @return [Array<String>]       An array of the example strings
        def to_examples(slots:[])
            raise StandardError, "The grammar must have at least one root rule" unless roots
            raise StandardError, "The grammar must contain at least one public rule" if roots.empty?

            roots.flat_map {|name, rule| expand_atom(rule, ["#{name}Intent"], slots:slots) }
        end

        # Expand an {Atom} into an array of strings
        # @return [Array]
        def expand_atom(atom, prefix=[], slots:[], slot_name:nil)
            case atom
                when JSGF::Alternation
                    atom.map {|a| expand_atom(a, prefix, slots:slots, slot_name:slot_name) }
                when JSGF::Atom
                    if prefix.first.is_a?(Array)
                        prefix.map {|pref| expand_atom(atom, pref, slots:slots, slot_name:slot_name) }
                    else
                        atom_name = atom.to_s
                        atom_name = "{#{atom_name}|#{slot_name}}" if slot_name && !atom_name.empty?
                        atom_name = nil if atom_name.empty?
                        [[*prefix, atom_name].compact.join(' ')]
                    end
                when JSGF::Rule, Array
                    atom.reduce(prefix) {|memo, a| expand_atom(a, memo, slots:slots, slot_name:slot_name)}
                when Hash
                    reference_name = atom[:name]
                    slot_name = slots.include?(reference_name) ? reference_name : nil
                    expand_atom(rules[atom[:name]], prefix, slots:slots, slot_name:slot_name)
                else
                    raise "Unknown atom #{atom}"
            end
        end
    end
end

# Example grammar. Replace this with your actual grammar.
grammar = JSGF.grammar 'ColorExpert' do
    rule MyColorIs: 'my favorite color is :Color'
    rule Color: %w{green red blue orange gold silver yellow black white}
end

File.write('utterances.txt', grammar.to_examples(slots:['Color']))