On 11/19/2012 04:43 AM, Pierpaolo Bernardi wrote:
#lang typed/racket
(define-type (Array a) (Rec AA (U (Vectorof a) (Vectorof AA))))
(: make-array (All (a) ((Listof Positive-Index) a -> (Array a))))
(define (make-array dims init)
(let loop ((dims dims))
(match dims
((list first)
(make-vector first init))
((list-rest first rest)
(let ((v (make-vector first)))
(for ((i (in-range first)))
(vector-set! v i (loop rest)))
v)))))
When `make-vector' is given one argument, it constructs a (Vectorof
Integer), namely #(0 0 0 ...). In this case you need to construct it
with the type (Vectorof (Array a)).
This works for me, on 5.3.1:
(let: ((v : (Vectorof (Array a)) (make-vector first (vector init))))
...)
Also, you should know that with a recursive type like that, you'll often
have a hard time convincing TR that you're dealing with a base case in a
particular loop iteration. You may end up passing predicates around to
identify instances of the type `a'.
If you want to know whether you'll have trouble, try writing
`array-flatten', with this type:
(All (a) ((Array a) -> (Vectorof a)))
If you can't, try this type:
(All (a) ((Array a) (Any -> Boolean : a) -> (Vectorof a)))
which is for an `array-flatten' that additionally accepts a predicate as
an argument.
Neil ⊥
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