Make flex directly generate the yylex method with parameter

Author: mdhooge

mc_lexer.l

@@ -1,8 +1,11 @@
 %{
 /* C++ string header, for string ops below */
 #include <string>
+
 /* Implementation of yyFlexScanner */ 
 #include "mc_scanner.hpp"
+#undef  YY_DECL
+#define YY_DECL int MC::MC_Scanner::yylex(MC::MC_Parser::semantic_type *lval)
 
 /* typedef to make the returns for the tokens shorter */
 typedef MC::MC_Parser::token token;
@@ -25,6 +28,10 @@ typedef MC::MC_Parser::token token;
 %option c++
 
 %%
+%{          // Code executed at the beginning of yylex
+            yylval = lval;
+%}
+
 [a-z]       { 
                return( token::LOWER );     
             }

mc_scanner.hpp

@@ -15,16 +15,11 @@ class MC_Scanner : public yyFlexLexer{
    MC_Scanner(std::istream *in) : yyFlexLexer(in),
                                   yylval( nullptr ){};
 
-   int yylex(MC::MC_Parser::semantic_type *lval)
-   {
-      yylval = lval;
-      return( yylex() ); 
-   }
-   
+   int yylex(MC::MC_Parser::semantic_type *lval);
+   // YY_DECL defined in mc_lexer.l
+   // Method body created by flex in mc_lexer.yy.cc
 
 private:
-   /* hide this one from public view */
-   int yylex();
    /* yyval ptr */
    MC::MC_Parser::semantic_type *yylval;
 };