Define a primitive data type: Difference between revisions

=={{header|Racket}}==

Most Racket programmers will use contracts to enforce additional guarantees on values. In the following example, the program exports <tt>x</tt> with a contract that ensures it is a number between 1 and 10.

<lang racket>

#lang racket

(provide (contract-out [x 1-to-10/c]))

(define 1-to-10/c (between/c 1 10))

(define x 5)

</lang>

In Typed Racket, it is possible to define a type that only contains the integers from 1 to 10. However, this type is inconvenient to use and is unlikely to be used in practice.

<lang racket>

#lang typed/racket

(define-type 1UpTo10 (U 1 2 3 4 5 6 7 8 9 10))

;; type-checks

(: x 1UpTo10)

(define x 3)

;; does not type-check

(: y 1UpTo10)

(define y 18)

</lang>