gistfile1.rkt

#lang typed/racket

(define-type (Even A) (U Null (Pairof A (Odd A))))
(define-type (Odd A) (Pairof A (Even A)))

(: even-lst (Even Integer))
(define even-lst '(1 2 3 4))

(: odd-lst (Odd Integer))
(define odd-lst '(1 2 3))

(: even->odd (All (A) (A (Even A) -> (Odd A))))
(define (even->odd elem lst)
  (cons elem lst))

(provide even->odd Even Odd
         even-lst odd-lst)

gistfile2.txt

-> (even->odd 1 '(1))
; even->odd: contract violation
;   expected: pair?
;   given: '()
;   in: the cdr of
;       a disjunct of
;       the 2nd argument of
;       (->
;        any/c
;        (recursive-contract
;         (or/c
;          null?
;          (cons/c
;           any/c
;           (recursive-contract
;            (cons/c ctc27 (Even122 ctc27))
;            #:chaperone)))
;         #:chaperone)
;        (recursive-contract
;         (cons/c
;          any/c
;          (recursive-contract
;           (or/c
;            null?
;            (cons/c ctc35 (Odd230 ctc35)))
;           #:chaperone))
;         #:chaperone))
;   contract from:
;       <collects>/tests/typed-racket/even-odd.rkt
;   blaming: top-level
;   at: <collects>/tests/typed-racket/even-odd.rkt:27.9
; [,bt for context]