[HACKERS] Question about Parser()

[Bin Liu]

Can somebody explain how the 'parsetree' in the parser( ) function get populated? What I saw is just a NIL. And it is not touched else where in this file.   This file is src/backend/parser/parser.c   Thanks!   Bin   /*  * parser  *  Given a query in string form, and optionally info about  *  parameter types, do lexical and syntactic analysis.  *  * Returns a list of raw (un-analyzed) parse trees.  */ List * parser(StringInfo str, Oid *typev, int nargs) {  int   yyresult;    parsetree = NIL;   /* in case parser forgets to set it */  have_lookahead = false;    scanner_init(str);  parser_init();  parse_expr_init();  parser_param_set(typev, nargs);    yyresult = yyparse();    scanner_finish();  clearerr(stdin);    if (yyresult)    /* error */   return NIL;    return parsetree; }