diff --git a/lib/propane/generator.rb b/lib/propane/generator.rb
index c086cf5..b89e667 100644
--- a/lib/propane/generator.rb
+++ b/lib/propane/generator.rb
@@ -28,6 +28,7 @@ class Propane
     def process_grammar!
       tokens_by_name = {}
       @grammar.tokens.each do |token|
+        # Check for token name conflicts.
         if tokens_by_name.include?(token.name)
           raise Error.new("Duplicate token name #{token.name.inspect}")
         end
@@ -35,9 +36,11 @@ class Propane
       end
       rule_sets = {}
       @grammar.rules.each do |rule|
+        # Check for token/rule name conflict.
         if tokens_by_name.include?(rule.name)
           raise Error.new("Rule name collides with token name #{rule.name.inspect}")
         end
+        # Build rule sets of all rules with the same name.
         @_rule_set_id ||= @grammar.tokens.size
         unless rule_sets[rule.name]
           rule_sets[rule.name] = RuleSet.new(rule.name, @_rule_set_id)
@@ -46,9 +49,17 @@ class Propane
         rule.rule_set = rule_sets[rule.name]
         rule_sets[rule.name] << rule
       end
+      # Check for start rule.
       unless rule_sets["Start"]
         raise Error.new("Start rule not found")
       end
+      # Generate lexer user code IDs for lexer patterns with user code blocks.
+      @grammar.patterns.select do |pattern|
+        pattern.code
+      end.each_with_index do |pattern, code_id|
+        pattern.code_id = code_id
+      end
+      # Map rule components from names to Token/RuleSet objects.
       @grammar.rules.each do |rule|
         rule.components.map! do |component|
           if tokens_by_name[component]
@@ -61,7 +72,9 @@ class Propane
         end
       end
       determine_possibly_empty_rulesets!(rule_sets)
+      # Generate the lexer.
       @lexer = Lexer.new(@grammar.patterns)
+      # Generate the parser.
       @parser = Parser.new(@grammar, rule_sets, rule_sets["Start"], @log)
     end
 
diff --git a/lib/propane/grammar.rb b/lib/propane/grammar.rb
index acfc6b6..06e5d2b 100644
--- a/lib/propane/grammar.rb
+++ b/lib/propane/grammar.rb
@@ -12,7 +12,6 @@ class Propane
       @patterns = []
       @tokens = []
       @rules = []
-      @code_id = 0
       @line_number = 1
       @next_line_number = @line_number
       @input = input.gsub("\r\n", "\n")
@@ -78,15 +77,12 @@ class Propane
         end
         pattern ||= name
         consume!(/\s+/)
-        if code = parse_code_block!
-          code_id = @code_id
-          @code_id += 1
-        else
+        unless code = parse_code_block!
           consume!(/;/, "expected pattern or `;' or code block")
         end
         token = Token.new(name: name, id: @tokens.size, line_number: @line_number)
         @tokens << token
-        pattern = Pattern.new(pattern: pattern, token: token, line_number: @line_number, code: code, code_id: code_id)
+        pattern = Pattern.new(pattern: pattern, token: token, line_number: @line_number, code: code)
         @patterns << pattern
       end
     end
@@ -132,9 +128,7 @@ class Propane
         unless code = parse_code_block!
           raise Error.new("Line #{@line_number}: expected code block to follow pattern")
         end
-        code_id = @code_id
-        @code_id += 1
-        @patterns << Pattern.new(pattern: pattern, line_number: @line_number, code: code, code_id: code_id)
+        @patterns << Pattern.new(pattern: pattern, line_number: @line_number, code: code)
       end
     end
 
diff --git a/lib/propane/pattern.rb b/lib/propane/pattern.rb
index a8f678b..40688b0 100644
--- a/lib/propane/pattern.rb
+++ b/lib/propane/pattern.rb
@@ -8,7 +8,7 @@ class Propane
 
     # @option options [Integer, nil] :code_id
     #   Code block ID.
-    attr_reader :code_id
+    attr_accessor :code_id
 
     # @return [String, nil]
     #   Pattern.
@@ -32,8 +32,6 @@ class Propane
     #   Optional parameters.
     # @option options [String, nil] :code
     #   Code block to execute when the pattern is matched.
-    # @option options [Integer, nil] :code_id
-    #   Code block ID.
     # @option options [Boolean] :drop
     #   Whether this is a drop pattern.
     # @option options [String, nil] :pattern
@@ -44,7 +42,6 @@ class Propane
     #   Line number where the token was defined in the input grammar.
     def initialize(options)
       @code = options[:code]
-      @code_id = options[:code_id]
       @drop = options[:drop]
       @pattern = options[:pattern]
       @token = options[:token]
diff --git a/spec/propane/grammar_spec.rb b/spec/propane/grammar_spec.rb
index 7604e49..8f159ce 100644
--- a/spec/propane/grammar_spec.rb
+++ b/spec/propane/grammar_spec.rb
@@ -41,7 +41,6 @@ EOF
       expect(o).to_not be_nil
       expect(o.pattern).to eq "while"
       expect(o.line_number).to eq 6
-      expect(o.code_id).to be_nil
       expect(o.code).to be_nil
 
       o = grammar.tokens.find {|token| token.name == "id"}
@@ -53,7 +52,6 @@ EOF
       expect(o).to_not be_nil
       expect(o.pattern).to eq "[a-zA-Z_][a-zA-Z_0-9]*"
       expect(o.line_number).to eq 9
-      expect(o.code_id).to be_nil
       expect(o.code).to be_nil
 
       o = grammar.tokens.find {|token| token.name == "token_with_code"}
@@ -65,7 +63,6 @@ EOF
       expect(o).to_not be_nil
       expect(o.pattern).to eq "token_with_code"
       expect(o.line_number).to eq 11
-      expect(o.code_id).to eq 0
       expect(o.code).to eq "Code for the token\n"
 
       o = grammar.tokens.find {|token| token.name == "token_with_no_pattern"}
@@ -79,7 +76,6 @@ EOF
       expect(o).to_not be_nil
       expect(o.line_number).to eq 17
       expect(o.token).to be_nil
-      expect(o.code_id).to be_nil
       expect(o.code).to be_nil
 
       expect(grammar.rules.size).to eq 3
@@ -128,7 +124,6 @@ EOF
 
       o = grammar.patterns.find {|pattern| pattern.token == o}
       expect(o).to_not be_nil
-      expect(o.code_id).to eq 0
       expect(o.code).to eq "  a = b;\n  return c;\n"
 
       o = grammar.tokens.find {|token| token.name == "code2"}
@@ -138,7 +133,6 @@ EOF
 
       o = grammar.patterns.find {|pattern| pattern.token == o}
       expect(o).to_not be_nil
-      expect(o.code_id).to eq 1
       expect(o.code).to eq %[  writeln("Hello there");\n]
     end
   end