On May 25, 2011, at 12:53 PM, Sam Tobin-Hochstadt wrote: > On Wed, May 25, 2011 at 12:27 PM, John Clements > <cleme...@brinckerhoff.org> wrote: >> Is there a "best-practice" model for type-case-like things in typed racket >> yet? Obvious choices: >> >> - tagged-list style, it's all a big cond but I have to use first, second, >> etc to refer to fields >> - struct-union style, feels better but I don't get to use match (IIUC). > > `match' and unions of structs should work fine together in Typed Racket.
Forgive me; I checked the docs & didn't see anything for 'match', but I see now
that it works as I'd expect.
Thanks!
Hang on, here's another question.
I see that typed racket doesn't signal an error on a match that doesn't have
clauses for all possible inputs, which is entirely reasonable; since that will
signal an error, that code should typecheck fine.
However, I might *want* typed racket to check that for me. I managed to come
up with this grozzz hack:
(: g ((U Number False) -> Number))
(define (g x)
(cond [(number? x) (+ x 4)]
[(false? x) 13]
;; type of x is now uninhabitable, so no typechecking error
[else (begin (string-append x "abc") (error 'foo))]))
In this case, when I comment out the 'false?' clause, the bogus clause suddenly
is type-checked (because x's type is no longer the empty union), and I get an
error.
So... I can get what I want, but in a very icky way. Is there a different and
more elegant way to force typed racket to check that I'm not failing to match?
John
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