define-enum.rkt

#lang racket
(define-syntax (define-enum stx)
  (syntax-case stx ()
    [(_ case-name contract-name id ...)
     (with-syntax ([(code ...) (generate-temporaries #'(id ...))])
       #'(begin (define-syntax case-name
                  (syntax-rules (id ...)
                    [(_ val [(id) code] ...)
                     (case val
                       [(id) code]
                       ...)]))
                (define contract-name (or/c 'id ...))))]))

(define-enum case/foo foo/c a b)
(define-enum case/bar bar/c a b c)

(define/contract (f-foo v)
  (-> foo/c number?)
  (case/foo v
    [(a) 1]
    [(b) 2]))

(define/contract (f-bar v)
  (-> bar/c number?)
  (case/bar v
    [(a) 10]
    [(b) 20]
    [(c) 30]))

(f-foo 'a)
(f-bar 'c)

;; throws error, as expected
(f-foo 'c)