1 files changed, 31 insertions, 0 deletions
diff --git a/src/util.ts b/src/util.ts
new file mode 100644
index 0000000..5556f70
--- /dev/null
+++ b/src/util.ts
@@ -0,0 +1,31 @@
+export type Op = string | { op: string; a: Op; b: Op };
+
+export type Rewrite<left extends Op, right extends Op> = {
+  type: 'rewrite';
+  left: left;
+  right: right;
+};
+
+export type Flip<R extends Rewrite<Op, Op>> = Rewrite<R['right'], R['left']>;
+
+export type ApplyRewrite<O extends Op, R extends Rewrite<Op, Op>> =
+  O extends R['left'] ? R['right']
+  : O extends string ? O
+  : O extends { a: Op, b: Op, op: string } ? (
+    ApplyRewrite<O['a'], R> extends O['a']
+    ? Omit<O, 'b'> & { b: ApplyRewrite<O['b'], R> }
+    : Omit<O, 'a'> & { a: ApplyRewrite<O['a'], R> }
+  )
+  : never;
+
+// interface Kind<V = unknown> {
+//   _: V;
+//   return: unknown;
+// }
+// type Ap<K extends Kind, V> = (K & { _: V })['return'];
+
+export type ChainRewrites<Rws extends Rewrite<Op, Op>[], O extends Op> =
+  Rws extends [] ? O
+   : Rws extends [infer R extends Rewrite<Op, Op>, ...infer Rs extends Rewrite<Op, Op>[]]
+   ? ChainRewrites<Rs, ApplyRewrite<O, R>>
+   : never;