I have the following simple module that I'm converting to typed/racket. I got a
type check error that I don't know how to fix. More specifically, it's related
to the polymorphic function dynamic-wind's arguments. I read from document [1]
that type inference doesn't work for a lambda that is an argument to a
polymorphic function. But since here the three arguments are all thunks
(without input argument), I don't know how to properly annotate them.
Note that I tried to even annotate the first argument:
(λ () (ann #f AnyValues))
And the type checker complained:
Argument 1:
Expected: (-> AnyValues)
Given: (-> AnyValues)
which is really weird.
[1]:
https://docs.racket-lang.org/ts-guide/more.html#%28part._when-annotations~3f%29
Here's the module:
------------------
#lang typed/racket
;;(require racket/string racket/list racket/match racket/system racket/port
racket/function)
(provide execute)
(: execute (-> String * (Values String String)))
(define (execute . args)
(define cmdln (string-join args))
(displayln (format "running ~a" cmdln))
(match (process cmdln)
[(list out in pid err f)
(define cust (make-custodian))
(dynamic-wind
(λ () (ann #f AnyValues))
(thunk
(parameterize ([current-custodian cust])
(define buf_stdout (open-output-string))
(define buf_stderr (open-output-string))
(thread (λ () (copy-port out buf_stdout (current-output-port))))
(thread (λ () (copy-port err buf_stderr (current-error-port))))
(displayln (f 'status))
(f 'wait)
(values (get-output-string buf_stdout) (get-output-string
buf_stderr))))
(thunk (custodian-shutdown-all cust)))
]))
Here's the type error:
----------------------
. executor.rkt:14:5: Type Checker: Polymorphic function `dynamic-wind' could
not be applied to arguments:
Argument 1:
Expected: (-> AnyValues)
Given: (-> AnyValues)
Argument 2:
Expected: (-> a)
Given: (-> (values (String : (Top | Bot)) (String : (Top | Bot))))
Argument 3:
Expected: (-> AnyValues)
Given: (-> Void)
Result type: a
Expected result: (values String String)
in: (dynamic-wind (λ () (ann #f AnyValues)) (thunk (parameterize
((current-custodian cust)) (define buf_stdout (open-output-string)) (define
buf_stderr (open-output-string)) (thread (λ () (copy-port out buf_stdout
(current-output-port)))) (thread (λ () (copy-port err buf_stderr
(current-error-port)))) (displayln (f (quote status))) (f (quote wait)) (values
(get-output-string buf_stdout) (get-output-string buf_stderr)))) (thunk
(custodian-shutdown-all cust)))
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