2 files changed, 47 insertions, 0 deletions

diff --git a/src/algo/mod.rs b/src/algo/mod.rs
new file mode 100644
index 000000000..c1644d16d
--- /dev/null
+++ b/src/algo/mod.rs
@@ -0,0 +1 @@
+pub mod walk;
diff --git a/src/algo/walk.rs b/src/algo/walk.rs
new file mode 100644
index 000000000..86dd82cc9
--- /dev/null
+++ b/src/algo/walk.rs
@@ -0,0 +1,46 @@
+use SyntaxNodeRef;
+
+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)]
+enum WalkEvent<'a> {
+    Enter(SyntaxNodeRef<'a>),
+    Exit(SyntaxNodeRef<'a>),
+}
+
+fn walk<'a>(root: SyntaxNodeRef<'a>) -> impl Iterator<Item=WalkEvent<'a>> {
+    let mut done = false;
+    ::itertools::unfold(WalkEvent::Enter(root), move |pos| {
+        if done {
+            return None;
+        }
+        let res = *pos;
+        *pos = match *pos {
+            WalkEvent::Enter(node) => match node.first_child() {
+                Some(child) => WalkEvent::Enter(child),
+                None => WalkEvent::Exit(node),
+            },
+            WalkEvent::Exit(node) => {
+                if node == root {
+                    done = true;
+                    WalkEvent::Exit(node)
+                } else {
+                    match node.next_sibling() {
+                        Some(sibling) => WalkEvent::Enter(sibling),
+                        None => match node.parent() {
+                            Some(node) => WalkEvent::Exit(node),
+                            None => WalkEvent::Exit(node),
+                        }
+                    }
+                }
+            }
+        };
+        Some(res)
+    })
+}
+