The problem here is with the optional third argument to `hash-ref`. Typed Racket only allows `#f` or functions as the third argument. Plain Racket allows any non-function value as a default, or a function which is called to produce the default. Since "any non-function" is not expressible in Typed Racket, it's more restricted here.
The best option is to wrap the third argument in a thunk: `(lambda () 'other)`. As an aside, you probably don't want to use `cast` this extensively in your program. Sam On Tue, Apr 21, 2020 at 10:35 AM Hendrik Boom <[email protected]> wrote: > > In typed Racket I define a hashtable: > > (: vector-to-contract (HashTable TType CContract)) > > (define vector-to-contract > (make-hash > (cast '( > (_bytes . bytes?) > (_s8vector . s8vector?) > (_u16vector . u16vector?) > (_s16vector . s16vector?) > (_u32vector . u32vector?) > (_s32vector . s32vector?) > (_u64vector . u64vector?) > (_s64vector . s64vector?) > (_f32vector . f32vector?) > (_f64vector . f64vector?)) > (Listof (Pair TType CContract)) > ) > )) > > And then I try to look something up in it: > > ( hash-ref vector-to-contract (cast '_bytes TType) (cast 'other CContract)) > > and I am informed that I cannot, it seems, look up a value of type > TType in a hastable whose type indicates it looks up things of type > TType: > > Type Checker: Polymorphic function `hash-ref' could not be applied to > arguments: > Types: HashTableTop a (-> c) -> Any > HashTableTop a False -> Any > HashTableTop a -> Any > Arguments: (HashTable TType CContract) TType CContract > Expected result: AnyValues > in: (hash-ref vector-to-contract (cast (quote _bytes) TType) (cast > (quote other) CContract)) > > > How *does* one use hashtables in typed Racket? > > -- hendrik > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/racket-users/20200421143453.lauuqi3pb4fdgyhh%40topoi.pooq.com. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/CAK%3DHD%2BY-pc3Jfg4RgRmAPMqSUxUj8rJsm3np2eq2%2B-J5PWTO4Q%40mail.gmail.com.
