/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Do a simulated parse forward (a "parse ahead") from the current
* stack configuration using stored lookahead input and a virtual parse
* stack. Return true if we make it all the way through the stored
* lookahead input without error. This basically simulates the action of
* parse() using only our saved "parse ahead" input, and not executing any
* actions.
*
* @param debug should we produce debugging messages as we parse.
*/
protected bool try_parse_ahead(bool debug)
{
int act;
short lhs, rhs_size;
/* create a virtual stack from the real parse stack */
virtual_parse_stack vstack = new virtual_parse_stack(stack);
/* parse until we fail or get past the lookahead input */
for (;;)
{
/* look up the action from the current state (on top of stack) */
act = get_action(vstack.top(), cur_err_token().sym);
/* if its an error, we fail */
if (act == 0) return false;
/* > 0 encodes a shift */
if (act > 0)
{
/* push the new state on the stack */
vstack.push(act-1);
if (debug) debug_message("# Parse-ahead shifts Symbol #" +
cur_err_token().sym + " into state #" + (act-1));
/* advance simulated input, if we run off the end, we are done */
if (!advance_lookahead()) return true;
}
/* < 0 encodes a reduce */
else
{
/* if this is a reduce with the start production we are done */
if ((-act)-1 == start_production())
{
if (debug) debug_message("# Parse-ahead accepts");
return true;
}
/* get the lhs Symbol and the rhs size */
lhs = production_tab[(-act)-1][0];
rhs_size = production_tab[(-act)-1][1];
/* pop handle off the stack */
for (int i = 0; i < rhs_size; i++)
vstack.pop();
if (debug)
debug_message("# Parse-ahead reduces: handle size = " +
rhs_size + " lhs = #" + lhs + " from state #" + vstack.top());
/* look up goto and push it onto the stack */
vstack.push(get_reduce(vstack.top(), lhs));
if (debug)
debug_message("# Goto state #" + vstack.top());
}
}
}
protected bool try_parse_ahead(bool debug)
{
int act;
short lhs, rhs_size;
var vstack = new virtual_parse_stack(stack);
for (;;)
{
act = get_action(vstack.top(), cur_err_token().sym);
if (act == 0)
{
return(false);
}
if (act > 0)
{
vstack.push(act - 1);
if (debug)
{
debug_message("# Parse-ahead shifts Symbol #" +
cur_err_token().sym +
" into state #" +
(act - 1));
}
if (!advance_lookahead())
{
return(true);
}
}
else
{
if (-act - 1 == start_production())
{
if (debug)
{
debug_message("# Parse-ahead accepts");
}
return(true);
}
lhs = production_tab[-act - 1][0];
rhs_size = production_tab[-act - 1][1];
for (int i = 0; i < rhs_size; i++)
{
vstack.pop();
}
if (debug)
{
debug_message("# Parse-ahead reduces: handle size = " +
rhs_size +
" lhs = #" +
lhs +
" from state #" +
vstack.top());
}
vstack.push(get_reduce(vstack.top(), lhs));
if (debug)
{
debug_message("# Goto state #" + vstack.top());
}
}
}
}