predict_match.rb

module Liquidscript
  class Parser
    module PredictMatch
      
      # Makes a prediction based on a set of actions.  If the peek token
      # doesn't have an action, it will try the special action `:_`, and
      # then give up.  If it finds a corresponding action either time, it
      # will run the action.
      #
      # @param actions [Hash<Symbol => Symbol>]
      # @return [Object] the result of the compiliation.
      def predict(*params, actions)
        
        action = actions.fetch(peek) do
          actions.fetch(:_)
        end
        
        if action.respond_to?(:call)
          action.call(*params)
        else
          send(:"compile_#{action}", *params)
        end
      end
      
      # Matches the next token of the input.  If it is not of the
      # expected type, it raises a SyntaxError.  Otherwise, it returns
      # the token.
      #
      # @param name [Symbol] the token to match.
      # @return [Array] the token.
      # @raise SyntaxError if the peeked token is invalid.
      def match(name)
        if name == peek
          input.next
        else
          raise SyntaxError, "Unexpected token #{peek}"
        end
      end
      
      # Returns the type of the next token.
      #
      # @return [Symbol] the type of the next token.
      def peek
        input.peek[0]
      end
      
    end
  end
end