Hi, in non-typed racket, I can define a generalized Fibonacci sequence
X[n+k] = f(X[n], X[n+1], ...., X[n+k-1])
using the following code
#lang racket
(require racket/stream)
(define (gfib f xs)
(define (gfib_t xs)
(stream-cons (last xs) (gfib_t (append (cdr xs) (list (f xs))))))
(stream-append (drop-right xs 1) (gfib_t xs)))
(define (sum xs) (apply + xs))
;; Example of a (0, 1) initialized Fibonacci sequence
(define gfib20 (gfib sum '(0 1 )))
But using typed racket, the following code
#lang typed/racket
(require pfds/stream)
(define (sum [xs : (Listof Number)] ) (apply + xs))
(define (gfib [f : (-> (Listof Number) Number)] [xs : (Listof Number)] )
(define (gfib_t [ys : (Listof Number)] )
(stream-cons (last ys) (gfib_t (append (cdr ys) (list (f ys))))))
(stream-append (stream (drop-right xs 1)) (gfib_t xs)))
leads to error message
; /home/kiong-ge/Programming/Racket/typed_racket_test.rkt:8:11: Type
Checker: insufficient type information to typecheck. please add more type
annotations
; in: gfib_t
How should I set the type signature in the typed racket in order to get the
same result generated non-typed racket code ?
Thanks,
Kiong-Ge.
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