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Define a primitive data type: Difference between revisions
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=={{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>
=={{header|Retro}}==
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