Type-safe AVL trees in TypeScript
Original code: https://gist.github.com/matthieubulte/e58dc1a6add5e114de0328f57dd3f460
Motivation
I was curious if TypeScript's type system is expressive enough to support this usage. Also I knew that I will have bugs while translating the code, and wanted to see if they will be caught by the type checker. Surely enough a bug I did have a bug, because the bug was not related to the tree balancing it was not caught by the type system.
Observations
- some places needed explcit Same, pointing towards type inference failure.
- without
matchsyntax code is more akward. Typing out types and constructors separately is a hassle. - union types in TS can express intermediate unions like NonLeaf, which can express t.left without descructuring.
- hard to write randomTree function without full dependent types.
Build & Test
- build -
npm i && tsc -w - test -
node_modules/mocha/bin/mocha build/test.js