Trying to get my head around typed racket and higher order functions

[greadey]

Hi all,

I have a function - create-points- which takes two lists of Flonum and yields a list of vector pairs suitable for passing to Racket's plot function.

In un-typed code I can just do;

(define (create-points xs ys)

  (map vector xs ys))

and voila!  It works.  However the only way I have managed to get it to type check is by wrapping the vector function in a lambda;

(: create-points : (Listof Flonum) (Listof Flonum) -> (Listof (Vectorof Flonum))

(define (create-points xs ys)
  (map  (lambda ([x : Flonum] [y : Flonum]) (vector x y)) xs ys)).

I have tried using an inst form, but I cannot seem to get that to work. Question is thought, is wrapping the vector function in a lambda the only way to do this?

Cheers,

greadey

[Sorawee Porncharoenwase]

inst is the way to go. How did you use it? This seems to work fine for me.

#lang typed/racket

(: create-points : (Listof Flonum) (Listof Flonum) -> (Listof (Vectorof Flonum)))
(define (create-points xs ys)
  (map (inst vector Flonum) xs ys))

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[David Storrs]

I haven't used typed racket, so maybe this is pointless, but does this work for you?

(define/contract (create-points xs ys)
  (-> (listof flonum?) (listof flonum?) (listof (vector/c flonum? flonum?)))
  (map vector xs ys))

(create-points '(1.0 2.0 3.0) '(4.0 5.0 6.0))

; => '(#(1.0 4.0) #(2.0 5.0) #(3.0 6.0))