I have been working on fixing the feature that does the checking if a certain type meets the expectations, and there are tons of bugs in it for the edge cases. I'm guessing you are just triggering one of those right now, so I would file a bug.
In terms of docs, they were just added and so are visible on the pre release page: http://www.cs.utah.edu/plt/snapshots/current/doc/ts-reference/type-ref.html#%28part._.Other_.Type_.Constructors%29 On Sat, May 10, 2014 at 8:30 AM, Alexander D. Knauth <alexan...@knauth.org> wrote: > Is there a way of specifying filters in typed racket so that if it returns > true, it knows it’s a certain type, but if it returns false, it doesn’t mean > that it’s not that type (or the other way around). > > For example: > (: string-with-length-1? (Any -> Boolean : #:if-true String #:if-false (U > String Any))) > (define (string-with-length-1? x) > (if (string? x) > (one? (string-length x)) > #f)) > > I know there’s something like this somewhere. > > When I tried it, it gave me an error message (I expected that), but that > error message said something about #:+ and #:- > > After trying some stuff and guessing stuff from error messages, and just to > try it and see what happened, I tried this: > (: string-with-length-1? (Any -> Boolean : #:+ (String @ x) #:- ((U String > Any) @ x))) > (define (string-with-length-1? x) > (if (string? x) > (one? (string-length x)) > #f)) > And it gave me this weird error message: > . Type Checker: type mismatch; > mismatch in filter > expected: ((String @ x) | Top) > given: ((String @ x) | Top) in: (if (string? x) (one? (string-length x)) > #f) > > What? If it’s expecting ((String @ x) | Top), and I’m giving it ((String @ > x) | Top), then what’s the problem? > > And is there any documentation anywhere about this? > > > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users > ____________________ Racket Users list: http://lists.racket-lang.org/users
