[Flex-help] Flex/Readline

[David L. B. <dl...@um...>]

Hi,

I've taken the "Advanced Calculator" example from the Flex/Bison Oreilly 
book and made some minor modifications so that setting the debug does 
not cause a syntax error and I've added C style '()' and '{}' to the IF 
THEN ELSE and WHILE DO statements.  When compiled the calculator works 
exactly as I expect it to.  If instead of calling yyparse() from main I 
call a function I've defined in the third section of the scanner.l file  
called "call_readline()"

void call_readline()
{
     YY_BUFFER_STATE bp;
     char *f = readline(">>> ");
     add_history(f);
     bp = yy_scan_string(f);
     free(f);
     yy_switch_to_buffer(bp);

     yyparse();  /* eat the input */

     yy_delete_buffer(bp);
}

which I took from a posting by John Levine, the parser returns "error: 
syntax error" message.  I have added several print statements to the 
scanner and to the parser.  Here is a typical session:

 >>> 1  + 1
TOKEN: 1
PARSE: NUMBER
TOKEN:  +
TOKEN: 1
PARSE: NUMBER
PARSE: exp + exp
1: error: syntax error
 >>> 2 * 2
TOKEN: 2
PARSE: NUMBER
TOKEN:  *
TOKEN: 2
PARSE: NUMBER
PARSE: exp * exp
1: error: syntax error
 >>> ^C


I have no idea how to debug this.  If I call yyparse() from main the 
scanner and parser both work.  If I change the input from stdin to 
readline the scanner seems to work but, what is being forwarded to the 
parser seems to be different for identical input.

Can someone provide guidance?

Cheers,

David