> On May 27, 2016, at 1:50 PM, Alex Knauth <[email protected]> wrote: > > >> On May 27, 2016, at 4:24 PM, 'John Clements' via Racket Users >> <[email protected]> wrote: >> >> I have a funny case in TR where occurrence typing loses information about >> the type of a term: >> >> #lang typed/racket >> >> (: expand (Sexp -> Sexp)) >> (define (expand s) >> (match s >> [(list (? symbol? id) a ...) >> s])) >> >> This fails to type check, because the occurrence of āsā in the rhs of the >> match is no longer known to be an Sexp. > > In the latest snapshot versions, this type-checks. It might be because of the > addition of Andrew Kent's intersection types, because according to DrRacket > the type of the `s` in the body is: > > (Pairof Symbol (U Null (Pairof Sexp (ā© Sexp (Listof Any))))) > > which is a subtype of Sexp. > > For previous versions, a workaround I've used is to add an extra > `my-identity` function to fool it it so that it doesn't realize that I'm > applying a predicate to `s` or matching on it.
Excellent! Many thanks for both the workaround and the good news about intersection types! 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]. For more options, visit https://groups.google.com/d/optout.
