Actually I don't think this is an over sight. The null string is a String. And Path-String is Path U String, but (path-string? (string #\null)) => #f. Sent from a mobile device. <div class="gmail_quote">On Mar 21, 2012 5:14 PM, "John Clements" <<a href="mailto:clements@brinckerhoff.org">clements@brinckerhoff.org</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> On Mar 21, 2012, at 3:20 PM, Sam Tobin-Hochstadt wrote: > On Wed, Mar 21, 2012 at 5:36 PM, John Clements > <<a href="mailto:clements@brinckerhoff.org">clements@brinckerhoff.org</a>> wrote: >> It looks like 'path-string?' is not labeled as a discriminator type. >> >>> path-string? >> - : (Any -> Boolean) >> #<procedure:path-string?> >>> >> >> Is this just an oversight? > > Yes, that's just an oversight, although it's slightly more complicated > than you'd think (because `(path-string? (string #\null))' is #f). Well, I just made do with (define-predicate ps? Path-String?), so this certainly isn't a major problem. John _________________________ Racket Developers list: <a href="http://lists.racket-lang.org/dev" target="_blank">http://lists.racket-lang.org/dev</a> </blockquote></div>