> On Jul 12, 2016, at 4:50 PM, 'John Clements' via Racket Users
> <racket-users@googlegroups.com> wrote:
>
> lang typed/racket
>
> (: process-number (Integer -> (U 'both-odd 'not-both-odd)))
> (define (process-number n)
> (if (andmap is-odd? (list (sub1 n) (add1 n)))
> 'both-odd
> 'not-both-odd))
>
> (: is-odd? (Integer -> (U 'odd 'even)))
> (define (is-odd? n)
> (if (= (modulo n 2) 0)
> 'even
> 'odd))
>
> (process-number 13) ;; > returns ‘both-odd
> this program suggests that both 12 and 14 are odd numbers. Can you see the
> bug?
Obviously ‘odd and ‘even are both Truthy values in Typed Racket. This is not a
bug. This is proof that TR accommodates R.
Here is the fixed version:
#lang typed/racket
(: process-number (Integer -> (U 'both-odd 'not-both-odd)))
(define (process-number n)
(if (andmap (lambda ({x : Integer}) (eq? (is-odd? x) 'odd)) (list (sub1 n)
(add1 n)))
'both-odd
'not-both-odd))
(: is-odd? (Integer -> (U 'odd 'even)))
(define (is-odd? n)
(if (= (modulo n 2) 0)
'even
'odd))
(process-number 13)
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