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Comment by guerrilla | Hacker News Reader

> (the Int x)

I like the cute syntax for type annotations.

I had to double-take because CL also has a THE also for declaring types, but it's a bit different; THE declares the type of an expression, not a variable (there is a separate type declaration for variables).

so e.g. (the fixnum (+ x 1)) would assert that (+ x 1) produces a fixnum.

That is also the case in Carp, x being an expression here.

Ah, okay. So is there a way to declare that a variable will always be of a given type in Carp?

Carp is statically-typed with type inference so writing (the Int x) would be enough for the compiler to forbid any usage of x as another type. Writing (Int.+ x 1) would accomplish the same as Int.+ only accepts Int.

You can also annotate function with a type signature.

  (sig add (Fn [Int Int] Int))
  (defn add [x y] (+ x y))

Is the same as:

  (defn add [x y] (the Int (+ (the Int x) (the Int y))))

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