1 files changed, 78 insertions, 0 deletions

diff --git a/crates/syntax/src/ted.rs b/crates/syntax/src/ted.rs
new file mode 100644
index 000000000..8d6175ed9
--- /dev/null
+++ b/crates/syntax/src/ted.rs
@@ -0,0 +1,78 @@
+//! Primitive tree editor, ed for trees
+#![allow(unused)]
+use std::ops::RangeInclusive;
+
+use crate::{SyntaxElement, SyntaxNode};
+
+#[derive(Debug)]
+pub struct Position {
+    repr: PositionRepr,
+}
+
+#[derive(Debug)]
+enum PositionRepr {
+    FirstChild(SyntaxNode),
+    After(SyntaxElement),
+}
+
+impl Position {
+    pub fn after(elem: impl Into<SyntaxElement>) -> Position {
+        let repr = PositionRepr::After(elem.into());
+        Position { repr }
+    }
+    pub fn before(elem: impl Into<SyntaxElement>) -> Position {
+        let elem = elem.into();
+        let repr = match elem.prev_sibling_or_token() {
+            Some(it) => PositionRepr::After(it),
+            None => PositionRepr::FirstChild(elem.parent().unwrap()),
+        };
+        Position { repr }
+    }
+    pub fn first_child_of(node: impl Into<SyntaxNode>) -> Position {
+        let repr = PositionRepr::FirstChild(node.into());
+        Position { repr }
+    }
+    pub fn last_child_of(node: impl Into<SyntaxNode>) -> Position {
+        let node = node.into();
+        let repr = match node.last_child_or_token() {
+            Some(it) => PositionRepr::After(it),
+            None => PositionRepr::FirstChild(node),
+        };
+        Position { repr }
+    }
+}
+
+pub fn insert(position: Position, elem: impl Into<SyntaxElement>) {
+    insert_all(position, vec![elem.into()])
+}
+pub fn insert_all(position: Position, elements: Vec<SyntaxElement>) {
+    let (parent, index) = match position.repr {
+        PositionRepr::FirstChild(parent) => (parent, 0),
+        PositionRepr::After(child) => (child.parent().unwrap(), child.index() + 1),
+    };
+    parent.splice_children(index..index, elements);
+}
+
+pub fn remove(elem: impl Into<SyntaxElement>) {
+    let elem = elem.into();
+    remove_all(elem.clone()..=elem)
+}
+pub fn remove_all(range: RangeInclusive<SyntaxElement>) {
+    replace_all(range, Vec::new())
+}
+
+pub fn replace(old: impl Into<SyntaxElement>, new: impl Into<SyntaxElement>) {
+    let old = old.into();
+    replace_all(old.clone()..=old, vec![new.into()])
+}
+pub fn replace_all(range: RangeInclusive<SyntaxElement>, new: Vec<SyntaxElement>) {
+    let start = range.start().index();
+    let end = range.end().index();
+    let parent = range.start().parent().unwrap();
+    parent.splice_children(start..end + 1, new)
+}
+
+pub fn append_child(node: impl Into<SyntaxNode>, child: impl Into<SyntaxElement>) {
+    let position = Position::last_child_of(node);
+    insert(position, child)
+}