Functional Programming with TypeScript's Type System

Post by Waterluvian » Sun, Apr 16, 2023, 1:07 PM UTC

SirensOfTitan wrote: post #9

Waterluvian wrote: post #8

While no actual Turing machine’s tape is infinitely long, I found issues in TypeScript with how finite generics are. You have to define every possible count of generic arguments if you want to preserve their types. And if you go above that count your type system degrades. I think there’s also a maximum of 7 or so before it doesn’t work. Beyond that and the generic type widens. For example, Lodash enumerating types fo…

This was fixed in Typescript 4.0, with the introduction of variadic tuples: https://www.typescriptlang.org/docs/handbook/release-notes/t...

Post by ekvintroj » Sun, Apr 16, 2023, 1:41 PM UTC

Post by rendall » Sun, Apr 16, 2023, 2:16 PM UTC

foepys wrote: post #14

I don't get TypeScript's type system. It is obviously very powerful and can model very complex type constraints. But then you have stuff like this where it is not checking types as I would expect: interface Foo { bar: string; } const f = {bar: "foobar"} as Readonly ; function someFunc(): Foo { return f; // No error or warning, even with all strict flags enabled }

Post by PhilipRoman » Sun, Apr 16, 2023, 2:21 PM UTC

rendall wrote: post #15

foepys wrote: post #14

I don't get TypeScript's type system. It is obviously very powerful and can model very complex type constraints. But then you have stuff like this where it is not checking types as I would expect: interface Foo { bar: string; } const f = {bar: "foobar"} as Readonly ; function someFunc(): Foo { return f; // No error or warning, even with all strict flags enabled }

Sorry, I don't get it. What do you expect to happen here?

Post by anamexis » Sun, Apr 16, 2023, 2:22 PM UTC

ekvintroj wrote: post #13

Try to type a flatMap and then we talk.

    type ValueOrArray = T | Array>;
    type FlatMap = (array: Array, fn: (el: In) => ValueOrArray) => Array;