complete adding lex_fn

lib/propane/generator.rb

@@ -359,7 +359,7 @@ class Propane
     # @return [String]
     #   Lex function to use.
     def lex_fn
-      @grammar.custom_lex_fn || "#{@grammar.prefix}lex"
+      @grammar.lex_fn || "#{@grammar.prefix}lex"
     end
 
     # Get the parser value type for the start rule.

lib/propane/grammar.rb

@@ -6,7 +6,7 @@ class Propane
     IDENTIFIER_REGEX = /(?:[a-zA-Z]|_[a-zA-Z0-9])[a-zA-Z_0-9]*/
 
     attr_reader :context_user_fields
-    attr_reader :custom_lex_fn
+    attr_reader :lex_fn
     attr_reader :tree
     attr_reader :tree_prefix
     attr_reader :tree_suffix
@@ -70,7 +70,7 @@ class Propane
       elsif parse_comment_line!
       elsif @modeline.nil? && parse_mode_label!
       elsif parse_context_user_fields_statement!
-      elsif parse_custom_lex_fn!
+      elsif parse_lex_fn!
       elsif parse_tree_statement!
       elsif parse_tree_prefix_statement!
       elsif parse_tree_suffix_statement!
@@ -119,9 +119,9 @@ class Propane
       end
     end
 
-    def parse_custom_lex_fn!
-      if md = consume!(/custom_lex_fn\b\s*(\w+)\s*;/)
-        @custom_lex_fn = $1
+    def parse_lex_fn!
+      if md = consume!(/lex_fn\b\s*(\w+)\s*;/)
+        @lex_fn = md[1]
       end
     end