Type variables range only over types, and `(Values A B)` isn't a type. If your program type checked, then the following program would too:
(: my-force : (All (A) (-> A) -> A)) (define (my-force f) (let ([tmp : A (f)]) tmp)) (my-force (lambda () (values (void) (void))) but this program has a runtime error with the wrong number of values. Sam On Wed, Mar 18, 2015 at 4:48 PM, Benjamin Greenman <bl...@cornell.edu> wrote: > Today I got a surprising type error that I think is worth sharing. > > (: my-force (All (A) (-> (-> A) A)) > (define (my-force x) (x)) > > (my-force (lambda () (values (void) (void))) > ;; ERROR! 'my-force' cannot be applied to argument. > ;; expected "(-> A)", got "(-> (values Void Void))" > ;; result type "A", expected result "AnyValues" > > (inst my-force (Values Void Void)) > ;; Parse Error in type: "Values" is unbound > > That is all. I see now that Values is only allowed in result positions, but > I'd still expected this to work. > > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users > ____________________ Racket Users list: http://lists.racket-lang.org/users
