Contents

module Treetop
  class Protometagrammar
    class PrimaryExpressionBuilder < ParsingExpressionBuilder
      def build
        seq(optional(:prefix), rest) do        
          def value(grammar)
            if prefix.epsilon?
              rest.value(grammar)
            else
              prefix.value(rest.value(grammar))
            end
          end
        
          def prefix
            elements[0]
          end
        
          def rest
            elements[1]
          end
        end
      end
  
      def rest
        seq(primary_expression, optional(:suffix)) do
          def value(grammar)
            if suffix.epsilon?
              primary_expression.value(grammar)
            else
              suffix.value(primary_expression.value(grammar))
            end
          end
    
          def primary_expression
            elements[0]
          end
    
          def suffix
            elements[1]
          end
        end
      end
    
      def primary_expression
        choice parenthesized_ordered_choice,
               :terminal_symbol,
               :nonterminal_symbol
      end
        
      def parenthesized_ordered_choice
        seq('(', optional(:space), :ordered_choice, optional(:space), ')', :trailing_block) do
          def value(grammar)
            nested_value = nested_expression.value(grammar)
            unless trailing_block.epsilon? || nested_value.kind_of?(NodeInstantiatingParsingExpression)
              raise "Blocks can only follow node-instantiating parsing expressions such as sequences and terminal symbols."
            end
            return trailing_block.value(nested_expression.value(grammar))
          end

          def nested_expression
            elements[2]
          end
        
          def trailing_block
            elements[5]
          end
        end
      end
    end
  end
end

Version data entries

1 entries across 1 versions & 1 rubygems

Version	Path
treetop-0.1.0	lib/treetop/protometagrammar/primary_expression_builder.rb