must-return.rkt

#lang racket/base

(require racket/contract)

(define must-return/c
  (make-contract
   #:name 'must-return/c
   #:late-neg-projection
   (λ (blm)
     (λ (f neg)
       (λ args
         (define finished? #f)
         (dynamic-wind
           void
           (λ ()
             (begin0
               (apply f args)
               (set! finished? #t)))
           (λ ()
             (unless finished?
               (raise-blame-error blm
                                  #:missing-party neg
                                  f
                                  "procedure did not return")))))))))

(define/contract (g f)
  must-return/c
  (f))

(let/cc k
  (g (λ () (k 42))))