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Comment by willtim | Hacker News Reader

> That would imply that "foo(x: int)" is a string rather than a function

But foo(x : int) is a string! It literally reads "foo applied to x". In the function definition, it appears to be used as a left-hand-side pattern which is "matched". The definition is written as if to say, whenever the term foo(x) is encountered, use this definition here. At least, that was my expectation.

> Haskell doesn't use that notation either

OCaml does and Haskell once had a proposal to add it. Haskell type signatures are normally written separately, but it does support annotating patterns with the right extensions.

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No, foo(x: int) is not a string, it's not even an expression, it's not even an AST node. It's a fragment of the larger ast node

    fn foo(x: int) -> ReturnType {
        body
    }

The ast here splits into

    Function {
        name: foo
        signature: (x: int) -> ReturnType
        body: body
    }

I.e. the arrow binary op binds more tightly than the adjacency between foo and x: int. And the type of foo is a function, not a string.

A "better" way to write this (in that it breaks down the syntax into the order it is best understood) might be

    static foo: (Int -> ReturnType) = {
        let x = arg0;
        body
    }

Or to put it another way. Reading foo(x: int) as "foo applied to x" in this case is a mistake, because that's now how things bind. You should read that "foo is a (function that takes Int to String)". It's a syntactic coincidence that foo and x are beside eachother, nothing more.

That's a nice explanation of what's going on. My point remains that I found the syntax confusing though.

Ya, I'm not really going to defend the current syntax past "function syntax is hard".

It's mixing up assigning a global variable, specifying that variables type, and destructuring an argument list into individual arguments, in one line. I've played at making my own language, and this is one part that I've never been satisfied with.

Personally I'd probably at least go with a `foo = <anonymous function>` syntax to split out the assigning part. But that's spending "strangeness budget" because that's not how C/Python/Java do it, and I can understand the decision to not spend that budget here...

> But foo(x : int) is a string!

Can you say so decisively for a language with first-class functions?

You are quoting me out of context. In many languages, the term and/or pattern foo(x : int) is a string, if foo : int -> string.

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