mpledger@cti1.UUCP (Mark Pledger) (10/03/90)
Could somebody please give me a hand with a lex & yacc problem. I am
trying to build a small subset of the SQL language. For purposes of this
question my yacc grammer is defined below.
%start cmds
%%
cmds : select ';'
{
fprintf(stdout,"SQL syntax correct.\n");
}
;
select : SELECT sel_list
{
}
;
sel_list : sel_type
{
}
| sel_list ',' sel_type
{
}
;
sel_type : attr_name
{
}
;
attr_name : IDENTIFIER
{
}
;
%%
... and so on
My lex specifications are list below.
delimiters [ \t]
ws {delimiters}+
newline [\n]
letter [A-Za-z_]
int [0-9]+
string {letter}+
squote \'[^\'\n]*\'
dquote \"[^\"\n]*\"
quotes (squote|dquote)
%% /* RULES */
{quotes} {
yylval.string = yytext;
return(QUOTES);
}
";" {
yylval.string = yytext;
return(EOC);
}
"," {
yylval.string = yytext;
return(',');
}
"q" { /* interactive quit command */
yylval.string = yytext;
return( 0 );
}
{newline} {
lineno++;
}
{int} {
yylval.integer = atoi(yytext);
return(INT);
}
{ws} ; /* white space */
{string} { /* normal token */
yylval.string = yytext;
return(symlookup());
}
"/*" { skipcomment();
}
. { /* for testing only */
ECHO; exit(0);
}
%%
... and so on
This lex & yacc grammer works only part of the time. I have specified
in the yacc grammer to allow multiple attr_name's after the key word SELECT.
Using the following examples below, I seem to be getting an error when I
don't think I should. I have run the lex code as a seperate program and it
returns all valid tokens -- regardless of white space. However when using
the yacc grammer, white space becomes significant.
select sno; <--- this works ok
select sno,pno; <--- yyparse() returns a 1 if yacc grammer is
(1) sel_list : sel_type ',' sel_list
| sel_type
;
sel_type : attr_name;
attr_name: IDENTIFIER;
<---- but works ok if yacc grammer is
(2) sel_list : sel_list ',' sel_type
| sel_type
;
sel_type : attr_name;
attr_name: IDENTIFIER;
select sno, pno; <--- this works ok if yacc grammer is
is specified as (1) above.
I have read that using left recursion keeps the stack space smaller for
yacc, so I am attempting to use it. But specifications (1) and (2) seem to
force a different syntax requirement (i.e., a space after the comma). Why
is this happening? Now when yacc does work for 2 attribute names, it does
not work for 3, 4, 5, 6, ... attributes. Why? I figured that if yacc
worked for 2 attribute parameters it would surely work for 5, 6, or 10. But
I found out it doesn't.
I have poured over three books (O'Reilly's Lex & Yacc, the dragon book,
and An Introduction to Compiler Contruction under Unix) and cannot find
anything similiar. Am I missing something? By the way I am using GNU's flex
and bison programs, but will be uploading them to a 3b2 running SYS5 v.3.2.
as soon as I get these darn things debugged.
Any help would be appriciated. Thanks in advance.
--
Sincerely,
Mark Pledger
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