/*
* paren_squish --
* replaces "parenthesized" plans in our search plan with "expr" nodes.
*/
PLAN *
paren_squish(PLAN *plan)
{
PLAN *expr; /* pointer to next expression */
PLAN *tail; /* pointer to tail of result plan */
PLAN *result; /* pointer to head of result plan */
result = tail = NULL;
/*
* the basic idea is to have yankexpr do all our work and just
* collect its results together.
*/
while ((expr = yankexpr(&plan)) != NULL) {
/*
* if we find an unclaimed ')' it means there is a missing
* '(' someplace.
*/
if (expr->execute == f_closeparen)
errx(1, "): no beginning '('");
/* add the expression to our result plan */
if (result == NULL)
tail = result = expr;
else {
tail->next = expr;
tail = expr;
}
tail->next = NULL;
}
return (result);
}
/*
* yankexpr --
* Removes one expression from the plan. This is used mainly by
* paren_squish. In comments below, an expression is either a
* simple node or a N_EXPR node containing a list of simple nodes.
*/
static PLAN *
yankexpr(PLAN **planp) /* pointer to top of plan (modified) */
{
PLAN *next; /* temp node holding subexpression results */
PLAN *node; /* pointer to returned node or expression */
PLAN *tail; /* pointer to tail of subplan */
PLAN *subplan; /* pointer to head of ( ) expression */
/* first pull the top node from the plan */
if ((node = yanknode(planp)) == NULL)
return (NULL);
/*
* If the node is an '(' then we recursively slurp up expressions
* until we find its associated ')'. If it's a closing paren we
* just return it and unwind our recursion; all other nodes are
* complete expressions, so just return them.
*/
if (node->type == N_OPENPAREN)
for (tail = subplan = NULL;;) {
if ((next = yankexpr(planp)) == NULL)
err(1, "(: missing closing ')'");
/*
* If we find a closing ')' we store the collected
* subplan in our '(' node and convert the node to
* a N_EXPR. The ')' we found is ignored. Otherwise,
* we just continue to add whatever we get to our
* subplan.
*/
if (next->type == N_CLOSEPAREN) {
if (subplan == NULL)
errx(1, "(): empty inner expression");
node->p_data[0] = subplan;
node->type = N_EXPR;
node->eval = f_expr;
break;
} else {
if (subplan == NULL)
tail = subplan = next;
else {
tail->next = next;
tail = next;
}
tail->next = NULL;
}
}
return (node);
}
