ast: implement postorder ast traversal

lang/ast/iterate.c

@@ -1,18 +1,18 @@
-#include <ivy/lang/ast.h>
 #include "node.h"
 
-enum ivy_status ivy_ast_node_iterate(
-	struct ivy_ast_node *node,
-	struct ivy_ast_node_iterator *it,
+#include <ivy/lang/ast.h>
+
+enum ivy_status iterate_regular(
+	struct ivy_ast_node *node, struct ivy_ast_node_iterator *it,
 	ivy_ast_node_iteration_callback callback)
 {
-	memset(it, 0x0, sizeof *it);
 	b_queue_push_back(&it->it_queue, &node->n_it.it_entry);
 	node->n_it.it_depth = 0;
 
 	while (!b_queue_empty(&it->it_queue)) {
 		b_queue_entry *entry = b_queue_first(&it->it_queue);
-		struct ivy_ast_node_iterator_entry *it_entry = b_unbox(struct ivy_ast_node_iterator_entry, entry, it_entry);
+		struct ivy_ast_node_iterator_entry *it_entry = b_unbox(
+			struct ivy_ast_node_iterator_entry, entry, it_entry);
 		node = b_unbox(struct ivy_ast_node, it_entry, n_it);
 
 		if (!node) {
@@ -37,17 +37,98 @@ enum ivy_status ivy_ast_node_iterate(
 	return IVY_OK;
 }
 
+enum ivy_status iterate_postorder(
+	struct ivy_ast_node *node, struct ivy_ast_node_iterator *it,
+	ivy_ast_node_iteration_callback callback)
+{
+	/* general iteration strategy:
+	 * 1. create a queue.
+	 * 2. push `node` to the end of the queue.
+	 * 3. for each node N in the queue:
+	 * 	1. collect N's children.
+	 * 	2. insert the children into the queue between N and the node
+	 * 	   immediately following N.
+	 * 4. the loop in step 3 continues over all nodes added within the loop,
+	 *    and stops when all nodes have been visited.
+	 * 5. iterate over the completed queue in reverse order, calling
+	 *    `callback` on each one.
+	 *
+	 * NOTES:
+	 *  - not sure how this will work for package definitions.
+	 *  - should probably use this just for the executable parts of the AST,
+	 *    not for nodes defining classes, function metadata, etc.
+	 */
+	b_queue_push_back(&it->it_queue, &node->n_it.it_entry);
+	node->n_it.it_depth = 0;
+
+	b_queue_iterator q_it;
+	b_queue_iterator_begin(&it->it_queue, &q_it);
+
+	while (b_queue_iterator_is_valid(&q_it)) {
+		struct ivy_ast_node_iterator_entry *it_entry = b_unbox(
+			struct ivy_ast_node_iterator_entry, q_it.entry, it_entry);
+		node = b_unbox(struct ivy_ast_node, it_entry, n_it);
+
+		if (!node) {
+			/* this should never happen. */
+			return IVY_ERR_INTERNAL_FAILURE;
+		}
+
+		const struct ast_node_type *type = get_ast_node_type(node->n_type);
+		if (type->n_collect_children) {
+			it->it_insert_after = q_it.entry;
+			type->n_collect_children(node, it);
+		}
+
+		b_queue_iterator_next(&q_it);
+	}
+
+	while (!b_queue_empty(&it->it_queue)) {
+		b_queue_entry *entry = b_queue_pop_back(&it->it_queue);
+		if (!entry) {
+			break;
+		}
+
+		node = b_unbox(struct ivy_ast_node, entry, n_it);
+
+		if (!node) {
+			/* this should never happen. */
+			return IVY_ERR_INTERNAL_FAILURE;
+		}
+
+		callback(node, it);
+	}
+
+	return IVY_OK;
+}
+
+enum ivy_status ivy_ast_node_iterate(
+	struct ivy_ast_node *node, struct ivy_ast_node_iterator *it,
+	enum ivy_ast_iterator_mode mode, ivy_ast_node_iteration_callback callback)
+{
+	memset(it, 0x0, sizeof *it);
+
+	switch (mode) {
+	case IVY_AST_ITERATE_REGULAR:
+		return iterate_regular(node, it, callback);
+	case IVY_AST_ITERATE_POSTORDER:
+		return iterate_postorder(node, it, callback);
+	default:
+		return IVY_ERR_INVALID_VALUE;
+	}
+}
+
 void ast_node_iterator_enqueue_node(
-	struct ivy_ast_node_iterator *it,
-	struct ivy_ast_node *parent,
+	struct ivy_ast_node_iterator *it, struct ivy_ast_node *parent,
 	struct ivy_ast_node *node)
 {
 	if (it->it_insert_after) {
-		b_queue_insert_after(&it->it_queue, &node->n_it.it_entry, it->it_insert_after);
+		b_queue_insert_after(
+			&it->it_queue, &node->n_it.it_entry, it->it_insert_after);
 	} else {
 		b_queue_push_back(&it->it_queue, &node->n_it.it_entry);
 	}
 
 	node->n_it.it_depth = parent->n_it.it_depth + 1;
 	it->it_insert_after = &node->n_it.it_entry;
-}
+}

lang/ast/iterate.h

@@ -2,8 +2,7 @@
 #define _AST_ITERATE_H_
 
 extern void ast_node_iterator_enqueue_node(
-	struct ivy_ast_node_iterator *it,
-	struct ivy_ast_node *parent,
+	struct ivy_ast_node_iterator *it, struct ivy_ast_node *parent,
 	struct ivy_ast_node *node);
 
-#endif
+#endif