Improve and abstract Cursor design. Start scanner

src/result.ts

@@ -0,0 +1,10 @@
+
+export type Result<T, E> =
+  | { tag: "ok", value: T }
+  | { tag: "error", error: E }
+
+export namespace Result {
+  export function ok<T, E>(value: T): Result<T, E> { return { tag: "ok", value } }
+  export function error<T, E>(error: E): Result<T, E> { return { tag: "error", error } }
+}
+