This repository contains some personal experiments with type-level programming in Typescript, mostly making use of ts-toolbelt. The end goal, which may or may not be ever reached, is to build an abstraction layer over Express to build fully type-safe REST APIs, largely inspired by Haskell's Servant.
Ideally, we would write something like this:
interface User {
id: number
name: string
}
const getUser: Endpoint<["api", "users", Capture<"id">, Handler<GET, [Response<200, User>, Response<404, string>]>>
// This type evaluates to (string) => [200, User] | [404, string]
= (id: string) => {
if (+id === 1) {
return [200, { id: 1, name: 'Test user' }];
} else {
return [404, 'User not found'];
}
}and have this generate the following code for Express:
app.get('/api/users/:id', (req, res) => {
const [code, res] = getUser(req.params.id);
res.status(code).json(res);
});
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