Add grammar syntax to specify lexer mode for tokens and patterns

lib/propane/grammar.rb

@@ -16,6 +16,7 @@ class Propane
       @code_blocks = []
       @line_number = 1
       @next_line_number = @line_number
+      @mode = nil
       @input = input.gsub("\r\n", "\n")
       parse_grammar!
     end
@@ -31,6 +32,7 @@ class Propane
     def parse_statement!
       if parse_white_space!
       elsif parse_comment_line!
+      elsif @mode.nil? && parse_mode_label!
       elsif parse_module_statement!
       elsif parse_class_statement!
       elsif parse_pattern_statement!
@@ -38,8 +40,7 @@ class Propane
       elsif parse_tokenid_statement!
       elsif parse_drop_statement!
       elsif parse_rule_statement!
-      elsif code = parse_code_block!
-        @code_blocks << code
+      elsif parse_code_block_statement!
       else
         if @input.size > 25
           @input = @input.slice(0..20) + "..."
@@ -48,6 +49,12 @@ class Propane
       end
     end
 
+    def parse_mode_label!
+      if md = consume!(/([a-zA-Z_][a-zA-Z_0-9]*)\s*:/)
+        @mode = md[1]
+      end
+    end
+
     def parse_white_space!
       consume!(/\s+/)
     end
@@ -61,6 +68,8 @@ class Propane
         md = consume!(/([\w.]+)\s*/, "expected module name")
         @modulename = md[1]
         consume!(/;/, "expected `;'")
+        @mode = nil
+        true
       end
     end
 
@@ -69,6 +78,8 @@ class Propane
         md = consume!(/([\w.]+)\s*/, "expected class name")
         @classname = md[1]
         consume!(/;/, "expected `;'")
+        @mode = nil
+        true
       end
     end
 
@@ -86,8 +97,10 @@ class Propane
         end
         token = Token.new(name, @line_number)
         @tokens << token
-        pattern = Pattern.new(pattern: pattern, token: token, line_number: @line_number, code: code)
+        pattern = Pattern.new(pattern: pattern, token: token, line_number: @line_number, code: code, mode: @mode)
         @patterns << pattern
+        @mode = nil
+        true
       end
     end
 
@@ -99,6 +112,8 @@ class Propane
         end
         token = Token.new(name, @line_number)
         @tokens << token
+        @mode = nil
+        true
       end
     end
 
@@ -110,7 +125,9 @@ class Propane
         end
         consume!(/\s+/)
         consume!(/;/, "expected `;'")
-        @patterns << Pattern.new(pattern: pattern, line_number: @line_number, drop: true)
+        @patterns << Pattern.new(pattern: pattern, line_number: @line_number, drop: true, mode: @mode)
+        @mode = nil
+        true
       end
     end
 
@@ -122,6 +139,8 @@ class Propane
         end
         components = components.strip.split(/\s+/)
         @rules << Rule.new(rule_name, components, code, @line_number)
+        @mode = nil
+        true
       end
     end
 
@@ -131,7 +150,17 @@ class Propane
         unless code = parse_code_block!
           raise Error.new("Line #{@line_number}: expected code block to follow pattern")
         end
-        @patterns << Pattern.new(pattern: pattern, line_number: @line_number, code: code)
+        @patterns << Pattern.new(pattern: pattern, line_number: @line_number, code: code, mode: @mode)
+        @mode = nil
+        true
+      end
+    end
+
+    def parse_code_block_statement!
+      if code = parse_code_block!
+        @code_blocks << code
+        @mode = nil
+        true
       end
     end
 

lib/propane/pattern.rb

@@ -26,6 +26,10 @@ class Propane
     #   Regex NFA for matching the pattern.
     attr_reader :nfa
 
+    # @return [String, nil]
+    #   Lexer mode for this pattern.
+    attr_reader :mode
+
     # Construct a Pattern.
     #
     # @param options [Hash]
@@ -40,12 +44,15 @@ class Propane
     #   Token to be returned by this pattern.
     # @option options [Integer, nil] :line_number
     #   Line number where the token was defined in the input grammar.
+    # @option options [String, nil] :mode
+    #   Lexer mode for this pattern.
     def initialize(options)
       @code = options[:code]
       @drop = options[:drop]
       @pattern = options[:pattern]
       @token = options[:token]
       @line_number = options[:line_number]
+      @mode = options[:mode]
       regex = Regex.new(@pattern)
       regex.nfa.end_state.accepts = self
       @nfa = regex.nfa