On Saturday, 15 February 2020 13:03:44 UTC, Jens Axel Søgaard wrote:
> Den lør. 15. feb. 2020 kl. 13.44 skrev greadey <gre...@gmail.com 
> <javascript:>>:
>> I have written a programme to compute a bootstrapped mean etc.  I 
>> successfully wrote it using lists both untyped and in typed/racket.
>> I am interested in optimising the code and having seen that typed racket 
>> performs faster (for lists) I am interested in seeing if I get a 
>> performance increase using vectors in both typed and untyped code.
>> In order to compute the median value as well as certain percentiles it is 
>> necessary to sort the samples.  My specific problem is using vector-sort.  
>> I have got round it by using vector->list and list->vector functions and 
>> using the list sort function.
>> If I use vector-sort typed racket keeps telling me to use 
>> "require/typed".  I got a function definition to compile  (:sort-myvector : 
>> (Vectorof Flonum) (Flonum Flonum -> Boolean) -> (Vectorof Flonum))
>> I'm not sure if that is exactly right but it was something similar, 
>> however it did not work.  I did add a "require/typed racket/vector" to the 
>> expression.
>> So, how can I use vector-sort in typed racket code, and can anyone tell 
>> me if translating vectors to lists and back again actually introduces a 
>> performance hit? 
> Here is an example of how to use `vector-sort` from a typed/racket program:
> #lang typed/racket
> (require/typed racket/vector
>   [vector-sort (-> (Vectorof Any) (-> Any Any Boolean) (Vectorof Any))])
> (define (compare x y)
>   (if (and (real? x) (real? y))
>       (< x y)
>       (error 'compare "expected two real numbers, got: ~a ~a" x y)))
> (vector-sort (vector 3 1 5 2) compare)
> /Jens Axel
> Thanks Jens - Nice one!  I had to define vector-sort to accept and yield 
Real values in order to get it to work!  My understanding of typed 
programming is that if you (as you did) define a function to be 
polymorphic, it should be polymorphic.  However, copying your code exactly 
and running vector sort  on a vector of reals gives  the error;
Type Checker: type mismatch
  expected: (Vectorof Any)
  given: (Vectorof Real) in: orig

Maybe one day I'll understand this one :-)

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