TypeScript vs Haskell

Structural vs Nominal Type Systems

TypeScript provides structural typing. If it walks like a duck, and quacks like a duck, for TypeScript, it is a duck. TypeScript does not care at all what name you give to the type.

Haskell provides nominal typing. It must be called a duck for it to be considered a duck. A rose by any other name won’t do.

Which of these two approaches are better? I think it too early, and too sweeping, a comparison to be valid.

TypeScript provides a gradual path to adding types to arguably the world’s most used and least learnt language: JavaScript. JavaScript is used by people from all sorts of backgrounds and motivations and programming experience level; perhaps the only thing they have in common is that nobody learns JavaScript, it is just hacked together until it works, with accompanying surprised Pikachu faces thrown around when the poor thing doesn’t work. This is the ecosystem TypeScript exists in.

Haskell users, as the old joke goes, all 50 of them, or 51 if I may immodestly count myself in, on the other hand are usually experienced programmers. They might not know the ancient scrolls of Hindley-Milner by heart, but that’s not for lack of trying. The goal of Haskell is to provide a laboratory for mathematics - it is the place where we can apply the abstract abstractions of category theory to find elegant primitives for domain specific data manipulation (aka, programming).

Both TypeScript and Haskell are based on solid, grounded, mathematics that goes back a century at least. It is not programmers hacking these languages together on whim and fashion (though that plays a part) - it is more of people trying to transmute the hard nuggets of type theory into practical programming languages.

Both TypeScript and Haskell provide type inference. Which means that you won’t need to tell the compiler the type of a duck or a rose, it’ll just know.

But the surprising thing is, after a while you’ll want to write the types. Programming in these languages then becomes the game of describing the types and how they transform into each other (as opposed to more direct approach of describing values and how they transform into each other).

Type systems nowadays are awesome! If you’re a programmer who thinks types are a pain, that “public static void main” ridiculousness, as I once was, I have hope for you – not only can things be much better, they’re also so much more fun.

Manav Rathi
Nov 2023