1 files changed, 38 insertions, 0 deletions

diff --git a/crates/ra_syntax/src/algo/walk.rs b/crates/ra_syntax/src/algo/walk.rs
new file mode 100644
index 000000000..536ee705f
--- /dev/null
+++ b/crates/ra_syntax/src/algo/walk.rs
@@ -0,0 +1,38 @@
+use {
+    SyntaxNodeRef,
+    algo::generate,
+};
+
+pub fn preorder<'a>(root: SyntaxNodeRef<'a>) -> impl Iterator<Item = SyntaxNodeRef<'a>> {
+    walk(root).filter_map(|event| match event {
+        WalkEvent::Enter(node) => Some(node),
+        WalkEvent::Exit(_) => None,
+    })
+}
+
+#[derive(Debug, Copy, Clone)]
+pub enum WalkEvent<'a> {
+    Enter(SyntaxNodeRef<'a>),
+    Exit(SyntaxNodeRef<'a>),
+}
+
+pub fn walk<'a>(root: SyntaxNodeRef<'a>) -> impl Iterator<Item = WalkEvent<'a>> {
+    generate(Some(WalkEvent::Enter(root)), move |pos| {
+        let next = match *pos {
+            WalkEvent::Enter(node) => match node.first_child() {
+                Some(child) => WalkEvent::Enter(child),
+                None => WalkEvent::Exit(node),
+            },
+            WalkEvent::Exit(node) => {
+                if node == root {
+                    return None;
+                }
+                match node.next_sibling() {
+                    Some(sibling) => WalkEvent::Enter(sibling),
+                    None => WalkEvent::Exit(node.parent().unwrap()),
+                }
+            }
+        };
+        Some(next)
+    })
+}