rec is Coalton’s named-recursion form, similar to Scheme’s “named-let”.

Syntax

(rec ⟨name⟩ (⟨binding⟩...)
  ⟨body⟩...)

;; ⟨binding⟩ := ⟨declare-form⟩
;;            | (⟨var⟩ ⟨init⟩)

Semantics

  • rec introduces a local recursive function ⟨name⟩ and immediately calls it with the initial values from the binding list.
  • rec is useful for iteration. The names go and % are common.
  • Init bindings may be declared with declare, like in let, let*, for, and for*.
  • Local declare forms in the binding list apply to init variables, which in turn constrain the recursive function’s parameters.
  • If you want to constrain the result type of a rec expression, wrap the whole form in the.
  • Recursive uses of ⟨name⟩ must be direct tail calls.
  • rec is intended for iteration. If you need more flexible local recursion, or want to pass the recursive function around as a value, use let together with fn instead.
  • ⟨body⟩ has an implicit progn.

Example

(the Integer
  (rec %
       ((declare i Integer)
        (declare acc Integer)
        (i n)
        (acc 0))
    (if (== i 0)
        acc
        (% (1- i) (+ acc i)))))