Starting to try Typed Racket for real. It's been really fun!
Overall the error messages have been clear and helpful. Only
a couple things so far have stumped me. Here's one.
Although this is fine:
(: h (HashTable Symbol String))
(define h (make-hash))
This is an error:
(: ph (Parameterof (HashTable Symbol String)))
(define ph (make-parameter (make-hash)))
; Type Checker: Polymorphic function `make-hash' could not be
applied to arguments:
; Domains: (Listof (Pairof a b))
;
; Arguments:
;
; in: (make-hash)
1. I don't understand why. Why does `(make-hash)` satisfy
`(HashTable Symbol String)` alone, but not wrapped in
`Parameterof`?
2. I'm not sure what the appropriate resolution is.
(a) Although this typechecks...
(: ph (Parameterof (HashTable Symbol String)))
(define ph (make-parameter (make-hash '([n/a . ""]))))
...it's a kludge.
(b) From the REPL I see that the type of `(make-hash)` is
`(HashTable Any Any)`. Although I _could_ try:
(: ph (Parameterof (U (HashTable Any Any)
(HashTable Symbol String))))
(define ph (make-parameter (make-hash )))
(i) that's not correct (why bother typing it Any/Any?)
(ii) that gives the same original type check error above
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