CODEWITHSUNDEEP
schemerackettyped-racket
Ben
Ben

Reputation: 5087

Local define usage in typed racket

I'm having a hard time figuring out how to use the local form in Typed Racket.

what is wrong with this: 

(: make-random-emetype-list (Range -> (Listof EmeType)))
(define (make-random-emetype-list range )
 (local ([define how-many-types (random-integer (Range-lower range) (Range-upper range))]
         [define: (bld-lst  lst remaining)  : ((Listof EmeType) Integer -> (Listof EmeType))
           (cond [(< remaining 1) lst]
                 [else (bld-lst (cons (new-emetype) lst) (- remaining 1))])])          
(bld-lst '() how-many-types)))

I'm sure the problem is that I don't quite follow the syntactic specification in the ts-reference, but it would be very helpful to have an example or two of a locally defined function in typed racket.

Upvotes: 1

Views: 140

Answers (1)

Ben
Ben

Reputation: 5087

The answer is, use letrec:. Well, now I know. 

(: make-random-emetype-list (Range -> (Listof EmeType)))
(define (make-random-emetype-list range )
  (letrec: ([lower : Integer (Range-lower range)]
        [upper : Integer (Range-upper range)]
        [how-many : Integer (random-integer lower upper)]
        [bld-lst : (Integer (Listof EmeType) -> (Listof EmeType)) (lambda: ([remaining : Integer] [lst : (Listof EmeType)]) 
                                                                    (cond [(< remaining 1 ) lst]
                                                                          [else (bld-lst (- remaining 1) (cons (new-emetype) lst))]))])
    (bld-lst how-many '())))

Upvotes: 1

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