On Saturday, 15 February 2020 13:03:44 UTC, Jens Axel Søgaard wrote:
>
> Den lør. 15. feb. 2020 kl. 13.44 skrev greadey >:
>
>> 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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