LEX & YACC

Constants, variables, and nodes can be represented by yylval in the parser’s value stack. Noticethe type definitions%token INTEGER%type exprThis binds expr to nPtr, and INTEGER to iValue in the YYSTYPE union. This is required so thatyacc can generate the correct code. For example, the ruleexpr: INTEGER { $$ = con($1); }should generate the following code. Note that yyvsp[0] addresses the top of the value stack, orthe value associated with INTEGER.yylval.nPtr = con(yyvsp[0].iValue);The unary minus operator is given higher priority than binary operators as follows:%left GE LE EQ NE '>' '