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Comment by sideeffffect | Hacker News Reader

It's been like this in the academia (Mathematics in particular) since ever.

Also, some people say that it makes for easier (less ambiguous?) parsing.

But the -> part is a bit weird. It "shouldn't" be

    def factorial(x: int) -> int:

but it "should" be

    def factorial(x: int): int =

Maybe it's that way because of Python?

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Some languages use the colon syntax, such as the Pascal family. Others, like Rust and Gleam, use the arrow syntax.

The arrow syntax meshes better with the idea that there's a difference between the types of values, and the meaning of a function signature. "foo: t" declares a name "foo" as having a type "t", but functions are abstractions — what is the "type" of factorial()? It's not "int".

The type of factorial() could be written:

    (int) -> int

or just:

    int -> int

If you look at the ML family as well as Haskell, that's exactly how they express it.

They do that for other reasons, too; those languages follow lambda calculus, which only has single-argument functions, so all functions are simply mappings between a single value to another value.

yes

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