On Sun, Oct 23, 2011 at 11:03 AM, Eric Tanter <etan...@dcc.uchile.cl> wrote: > So this seems the good way to go. > > However, of course, this does not work if the return type is compatible with > Void: > > (: f ((U String Integer) -> Any)) > (define (f x) > (cond > [(string? x) (string=? x "hi")] > [(exact-nonnegative-integer? x) (= x 7)])) > > typechecks. > > I wonder if there a trick to make this work in all cases. > Probably not with standard `cond', because as Ian suggested, this would > require to specify an else clause that returns something which is not a > subtype of Any. > > I guess you could include a type Invalid, which is NOT a subtype of Any. That > would make it possible to provide a special `cond' form for which the > proposed pattern would work (the else clause would be typed as Invalid). > Would something like that work?
Yes, I have planned to do this for a while. Probably the form it will take will be a macro that always produces a type error when checked, rather than a new type. Then macros could use this form to ensure exhaustiveness. -- sam th sa...@ccs.neu.edu _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
