There's an issue open about partition: https://github.com/racket/typed-racket/issues/138
Does `my-partition` work like you'd want? Based on Alex's last comment on the issue, it seems hard to give a predicate that matches the type. (Whenever I've wanted `partition` in typed code, I was always able to use 2 filters instead.) On 10/5/21, 'John Clements' via Racket Users <[email protected]> wrote: > I was somewhat surprised to see today that I can’t use a predicate with both > positive and negative propositions in the way I would expect with > partition: > >> (:print-type partition) > (All (a b) > (case-> > (-> (-> b Any : #:+ a) (Listof b) (values (Listof a) (Listof b))) > (-> (-> a Any) (Listof a) (values (Listof a) (Listof a))))) > > > Specifically, I would have expected the type to be something like this: > > (All (a b c) > (case-> > (-> (-> b Any : #:+ a) (Listof b) (values (Listof a) (Listof b))) > ;; the second list must consist of 'c's: > (-> (-> b Any : #:+ a #:- c) (Listof b) (values (Listof a) (Listof c))) > (-> (-> a Any) (Listof a) (values (Listof a) (Listof a))))) > > … so that if, say, I had a list of Elephants and Emus, that I could use > elephant? to split it into two lists: one of type (Listof Elephant) and one > of type (Listof Emu). > > I tried to roll my own, and got pretty close: > > (: my-partition > (All (a b c) > (case-> > ;; the second list must consist of 'c's: > (-> (-> b Any : #:+ a #:- c) (Listof b) (values (Listof a) (Listof > c))) > ))) > > (define (my-partition my-pred elts) > (cond [(empty? elts) > (values '() '())] > [else > (define-values (stacks non-stacks) > (my-partition my-pred (rest elts))) > (define f (first elts)) > (cond [(my-pred f) > (values (cons f stacks) > non-stacks)] > [else > (values stacks (cons f non-stacks))])])) > > That is, I can do it for the case-> clause that I care about. Putting the > other two back in there causes it to fail type-checking. Is that the > problem, that TR can’t accommodate both flavors in the same type? > > John > > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/racket-users/aa1e77a8-9cc4-4f99-b413-1304daeec12b%40mtasv.net. > -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/CAFUu9R6ncSV-MY%3DMDJjG%3DbsKVCjA3%3DDdGwJGNQfBVkTK70guqQ%40mail.gmail.com.
