This is now the fourth time I've seen people ask about this. Why can't Typed Racket be a little different than Racket and have another match form that does this or a notion of disjoint unions?
You've said many times that TR is for converting Racket programs, but clearly some of us want to write quasi-ML in TR, but we can't without hacks like this. Jay On Fri, Dec 9, 2011 at 1:29 PM, Sam Tobin-Hochstadt <sa...@ccs.neu.edu>wrote: > I think what you're asking for is static errors for coverage failures > in `match' when used in Typed Racket. > > There are two reasons this isn't something I'm planning on doing in > general: > 1. It would be a significant change from the semantics of `match' in > Racket, which as you note raises a runtime error. > 2. It's unlikely to be precise enough in enough cases to be useful. > `match' is just too flexible, and TR insufficiently smart, for this to > be the right default. > > However, for this purpose, Typed Racket provides the `typecheck-fail' > form [1], for raising explicit type errors. Rewrite your match > expression to: > > (match f > [(list s) #true] > [_ (typecheck-fail #'here #:covered-id f)]) > > and you get the error message: > Type Checker: Incomplete case coverage; missing coverage of Foo > > [1] > http://pre.racket-lang.org/docs/html/ts-reference/Utilities.html?q=type-e#%28form._%28%28lib._typed-racket/base-env/prims..rkt%29._typecheck-fail%29%29 > > On Fri, Dec 9, 2011 at 3:20 PM, <cleme...@brinckerhoff.org> wrote: > > *** Description: > > Code using match to take apart opaque types > > signal runtime match failure rather than > > a type-checking failure. > > > > -- > sam th > sa...@ccs.neu.edu > -- Jay McCarthy <j...@cs.byu.edu> Assistant Professor / Brigham Young University http://faculty.cs.byu.edu/~jay "The glory of God is Intelligence" - D&C 93
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