Rock paper scissors in 4 lines of typescript types (no javascript)

rock-paper-scissors-typescript.md

Rock paper scissors in 4 lines of typescript types (no javascript)

Thanks to @harrysolovay

type Rock = { b?: never, c?: unknown }
type Paper = { a?: unknown, c?: never }
type Scissors = { a?: never, b?: unknown }

type Beats<A extends B, B> = {} 

let a: Beats<Rock, Paper>     // will throw error eg in Beats<Rock, Paper>, but not in Beats<Paper, Rock>

Try it typescript playground

Turing complete

An amazing concept is that typescript types are Turing complete, so you can do jawdropping things like an SQL database implementation in just typescript types.