Values handling in non-function contexts causes errors #1409
Description
What version of Racket are you using?
8.14 [cs]
What program did you run?
- Using
Valuesin the return type oflet:
Welcome to Racket v8.14 [cs].
> (let #:∀ (a ...) ([thk : (→ (Values a ... a)) (λ () (values 1 2 3))])
(thk))
- : (values Integer Integer Integer) [more precisely: (Values One Positive-Byte Positive-Byte)]
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3
> (let #:∀ (a ...) ([thk : (→ (Values a ... a)) (λ () (values 1 2 3))]) : (Values a ... a)
(thk))
string:1:80: Type Checker: Error in macro expansion -- parse error in type;
type variable must be used with ...
variable: a
in: a
[,bt for context]Equivalent code that works by wrapping Values inside a function type:
> (: f (∀ (a ...) (→ (→ (Values a ... a)) (Values a ... a))))
> (define (f thk) (thk))
> (f (λ () (values 1 2 3)))
- : (values Integer Integer Integer) [more precisely: (Values One Positive-Byte Positive-Byte)]
1
2
3
> (: g (∀ (a ...) (→ (→ (Values a ... a)) (Values a ... a))))
> (define (g thk1)
(: thk2 (→ (Values a ... a)))
(define thk2 thk1)
(thk2))
> (g (λ () (values 1 2 3)))
- : (values Integer Integer Integer) [more precisely: (Values One Positive-Byte Positive-Byte)]
1
2
3- Using
Valuesinlet/cc:
Welcome to Racket v8.14 [cs].
> (require typed/racket/unsafe)
> (unsafe-require/typed racket/base
[call-in-continuation
(∀ (a ...)
(case→ (→ (→ a ... a Nothing) (→ (Values a ... a)) Nothing)
(→ (→ Any * Nothing) (→ AnyValues) Nothing)))])
> (: h (∀ (a ...) (→ (→ (Values a ... a)) (Values a ... a))))
> (define (h thk)
(let/cc k : (Values a ... a)
(call-in-continuation k thk)))
string:2:2: Type Checker: Polymorphic function `call/cc' could not be applied to arguments:
Types: (-> (-> Nothing) (values)) -> (values)
(-> (-> Nothing) (values)) Prompt-TagTop -> (values)
(-> (-> a c ... c Nothing) (values b c ... c)) -> (values (U a b) c ... c)
(-> (-> a c ... c Nothing) (values b c ... c)) Prompt-TagTop -> (values (U a b) c ... c)
Arguments: (-> (-> a ... a Nothing) Nothing)
Expected result: (values)
in: (let/cc k : (Values a ... a) (call-in-continuation k thk))
[,bt for context]A working alternative:
> (: i (∀ (a ...) (→ (→ (Values a ... a)) (→ (→ a ... a Nothing) (Values a ... a)))))
> (define ((i thk) k) (call-in-continuation k thk))
> (call/cc (i (λ () (values 1 2 3))))
- : (values Integer Integer Integer) [more precisely: (Values One Positive-Byte Positive-Byte)]
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