Hi, all.
Why does the following typecheck:
#lang typed/racket
(provide group)
(define #:forall (A)
(group [list : (Listof A)]
[count : Exact-Positive-Integer]) : (Listof (Listof A))
(: group-step (All (A) ((Listof A) (Listof A) (Listof (Listof A)) ->
(Listof (Listof A)))))
(define (group-step list group groups)
(cond [(and (empty? list) (empty? group)) groups]
[(empty? list) (cons (reverse group) groups)]
[(= (length group) count)
(group-step (rest list) `(,(first list)) (cons (reverse group)
groups))]
[else
(group-step (rest list) (cons (first list) group) groups)]))
(reverse (group-step list empty empty)))
But the following doesn't:
#lang typed/racket
(provide group)
(define #:forall (A)
(group [list : (Listof A)]
[count : Exact-Positive-Integer]) : (Listof (Listof A))
(define #:forall (A)
(group-step [list : (Listof A)]
[group : (Listof A)]
[groups : (Listof (Listof A))]) : (Listof (Listof A))
(cond [(and (empty? list) (empty? group)) groups]
[(empty? list) (cons (reverse group) groups)]
[(= (length group) count)
(group-step (rest list) `(,(first list)) (cons (reverse group)
groups))]
[else
(group-step (rest list) (cons (first list) group) groups)]))
(reverse (group-step list empty empty)))
(Notice the change in the declaration of the inner function's signature, inlined
in the `define' vs. separate on it's on `(: ...)'.)
The error message:
Type Checker: insufficient type information to typecheck. please add more
type annotations in: group-step
>From reading Typed Racket's reference, section 2.4 Definitions, I
thought the latter was another way of writing the former.
Thanks.
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