Function plpgsql_param_ref

src/pl/plpgsql/src/pl_comp.c:1170–1187

* plpgsql_param_ref parser callback for ParamRefs ($n symbols) */

 * plpgsql_param_ref		parser callback for ParamRefs ($n symbols)
 */
static Node *
plpgsql_param_ref(ParseState *pstate, ParamRef *pref)
{
	PLpgSQL_expr *expr = (PLpgSQL_expr *) pstate->p_ref_hook_state;
	char		pname[32];
	PLpgSQL_nsitem *nse;

	snprintf(pname, sizeof(pname), "$%d", pref->number);

	nse = plpgsql_ns_lookup(expr->ns, false,
							pname, NULL, NULL,
							NULL);

	if (nse == NULL)
		return NULL;			/* name not known to plpgsql */

	return make_datum_param(expr, nse->itemno, pref->location);
}

/*
 * resolve_column_ref		attempt to resolve a ColumnRef as a plpgsql var