On Jun 21, 2015, at 5:41 AM, Aidan Gauland <aidal...@slingshot.co.nz> wrote:
> Say I want to define a flat contract for the "freshness" field of my
> fish class, so I define a contract for it like so:
>
> (define/contract fish-freshness/c
> (-> any/c
> boolean?)
> (flat-named-contract 'fish-freshness/c
> (lambda (x)
> (not (eq? #f (member x '(fresh frozen edible rotten)))))))
>
> Am I barking up the wrong tree here, or is this perfectly sensible?
>
> Regards,
> Aidan Gauland
If this does what you want, it’s fine, but the define/contract is probably
unnecessary, and
(define fish-freshness/c
(flat-named-contract ‘fish-freshness/c
(lambda (x)
(not (eq? ….)))))
Should do what you want.
The flat-named-contract is also probably unnecessary (though it can be useful
if the name isn’t just a symbol), so
(define (fish-freshness/c x)
(not (eq? ….)))
Will also do what you want.
And finally, another way of doing this would be:
(define fish-freshness/c (or/c ‘fresh ‘frozen ‘edible ‘rotten))
Or if you prefer giving the contract a better name for error messages:
(define fish-freshness/c
(flat-named-contract ‘fish-freshness/c (or/c ‘fresh ‘frozen ‘edible ‘rotten)))
Any one of these is “sane” as long as they work, and it depends on which one
you think looks more readable, makes you’re intent clear, and gives error
messages that make sense.
I just finished this when I saw Matthias Felleisen’s reply. I’m sending it
anyway.
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