Hello,
My apologizes if this questions have already been answer in this list, I may
have missed.
I'm trying to make this expression work in typed/racket:
(map car '((1 . 2) (3 . 4)))
But if fails with the following type error:
; Type Checker: Polymorphic function `map' could not be
; applied to arguments:
; Domains: (-> a b ... b c) (Listof a) (Listof b) ... b
; (-> a c) (Pairof a (Listof a))
; Arguments: (All (a b) (case-> (-> (Pairof a b) a) (-> (Listof a) a))) (List
; (Pairof One Positive-Byte) (Pairof Positive-Byte Positive-Byte))
; in: (map car (quote ((1 . 2) (3 . 4))))
I tried annotating the type of the second argument to "map" like:
(: L (Listof (Pairof Any Any)))
(define L '((1 . 2) (3 . 4)))
Which type checks successfully, but then again I get the same error when
evaluating:
(map car L)
It seems to me that the type of "map":
map
- : (All (c a b ...)
(case->
(-> (-> a c) (Pairof a (Listof a)) (Pairof c (Listof c)))
(-> (-> a b ... b c) (Listof a) (Listof b) ... b (Listof c))))
and the type of "car":
car
- : (All (a b) (case-> (-> (Pairof a b) a) (-> (Listof a) a)))
Are compatible with the type of "L" - but I'm failing to understand the meaning
of the type check error message.
The empty list is the only expression that I was able to make it work in "(map
car <>)".
(map car '())
- : (Listof Any)
'()
Appreciate your help!
Best Regards
- Rodrigo
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