-> denotes a function type. You use it in declare forms, class method types, local declarations, and inline lisp type signatures.

Syntax

;; in types
⟨type-product⟩ [&key ...] -> ⟨type-product⟩

;; in Lisp forms

(lisp (-> ⟨type-product⟩) ...)

;; ⟨type-product⟩ := ⟨type⟩
;;                 | ⟨type-product⟩ * ⟨type⟩

Semantics

  • A -> B means a function from A to B.
  • A * B -> C means a fixed-arity two-argument function.
  • Void -> T is a true nullary function type.
  • T -> Void is a function type that returns no values.
  • In lisp forms, the arrow separates the output type list from the embedded Lisp variable list.
  • Keyword argument lists can precede ->.

Options

  • Put &key between positional inputs and -> to describe keyword arguments.
  • Use explicit forall when you want the type variables named in the signature to be in lexical scope inside the body.

Example

(coalton-toplevel
  (declare add2 (Integer -> Integer))
  (define (add2 x)
    (+ x 2)))