I'd like to play around with implementing generics or type classes in
Typed Racket, but without changing its internals, just to see what it
takes. I think I could get something pretty decent working if I could
get the following program to type:
(define ops-hash (make-hasheq))
(: set-ring-ops! (All (A) (Symbol (ring-ops A) -> Void)))
(define (set-ring-ops! name ops)
(hash-set! ops-hash name ops))
(: get-ring-ops (All (A) ((ring-member A) -> (ring-ops A))))
(define (get-ring-ops x)
(define name (ring-member-ops-name x))
(hash-ref ops-hash name (λ () (error 'get-ring-ops
"unregistered ring ~a"
name))))
Of course, I can't. In fact, I can't get this to work by writing
`set-ring-ops!' and `get-ring-ops' in untyped Racket and importing them
using `require/typed', because the contract system can't prove that the
`A' in `get-ring-ops' is the same as the `A' in `set-ring-ops!'.
Is there a secret, hidden escape hatch that would allow me to get
functions with these types and behaviors?
Neil ⊥
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