Hi,
The following program typechecks:
#lang typed/racket
(define-type R Real)
(define-type Rs (Listof R))
(define-type ROrRs (U R Rs))
(define (test [x : ROrRs]) : R
(if (list? x)
(if (null? x)
(error "Less than one")
(if (null? (cdr x))
(car x)
(error "More than one")))
x))
However, if we define R as an opaque type, e.g., using
(require/typed racket [#:opaque MyReal real?])
(define-type R MyReal)
then the program does not typecheck.
I was expecting that the program should typecheck independently of the
actual type being used for R. What am I missing?
António Leitão.
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