/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Procedure that attempts to fix a shift/reduce error by using
* precedences. --frankf 6/26/96
*
* if a production (also called rule) or the lookahead terminal
* has a precedence, then the table can be fixed. if the rule
* has greater precedence than the terminal, a reduce by that rule
* in inserted in the table. If the terminal has a higher precedence,
* it is shifted. if they have equal precedence, then the associativity
* of the precedence is used to determine what to put in the table:
* if the precedence is left associative, the action is to reduce.
* if the precedence is right associative, the action is to shift.
* if the precedence is non associative, then it is a syntax error.
*
* @param p the production
* @param term_index the index of the lokahead terminal
* @param parse_action_row a row of the action table
* @param act the rule in conflict with the table entry
*/
protected bool fix_with_precedence(
production p,
int term_index,
parse_action_row table_row,
parse_action act)
{
terminal term = terminal.find(term_index);
/* if the production has a precedence number, it can be fixed */
if (p.precedence_num() > assoc.no_prec)
{
/* if production precedes terminal, put reduce in table */
if (p.precedence_num() > term.precedence_num())
{
table_row.under_term[term_index] =
insert_reduce(table_row.under_term[term_index], act);
return(true);
}
/* if terminal precedes rule, put shift in table */
else if (p.precedence_num() < term.precedence_num())
{
table_row.under_term[term_index] =
insert_shift(table_row.under_term[term_index], act);
return(true);
}
else /* they are == precedence */
/* equal precedences have equal sides, so only need to
* look at one: if it is right, put shift in table */
{
if (term.precedence_side() == assoc.right)
{
table_row.under_term[term_index] =
insert_shift(table_row.under_term[term_index], act);
return(true);
}
/* if it is left, put reduce in table */
else if (term.precedence_side() == assoc.left)
{
table_row.under_term[term_index] =
insert_reduce(table_row.under_term[term_index], act);
return(true);
}
/* if it is nonassoc, we're not allowed to have two nonassocs
* of equal precedence in a row, so put in NONASSOC */
else if (term.precedence_side() == assoc.nonassoc)
{
table_row.under_term[term_index] = new nonassoc_action();
return(true);
}
else
{
/* something really went wrong */
throw new internal_error("Unable to resolve conflict correctly");
}
}
}
/* check if terminal has precedence, if so, shift, since
* rule does not have precedence */
else if (term.precedence_num() > assoc.no_prec)
{
table_row.under_term[term_index] =
insert_shift(table_row.under_term[term_index], act);
return(true);
}
/* otherwise, neither the rule nor the terminal has a precedence,
* so it can't be fixed. */
return(false);
}
