add documentation and a contract for send-url/mac

net-doc/net/scribblings/sendurl.scrbl

@@ -77,6 +77,18 @@ the @racket[#:delete-at] argument is @racket[#f], no eager deletion
 happens, but old temporary files are still deleted as described
 above.}
 
+@defproc[(send-url/mac [url string?]
+                       [#:browser browser (or/c string? #f) #f])
+         void?]{
+ Like @racket[send-url], but only for use on a Mac OS X machine.
+
+ The optional @racket[browser] argument, if present, should be the name
+ of a browser installed on the system. For example,
+ @racketblock[(send-url/mac "http://www.google.com/" #:browser "Firefox")]
+ would open the url in Firefox, even if that's not the default browser.
+ Passing @racket[#f] means to use the default browser.
+}
+
 @defparam[external-browser cmd browser-preference?]{
 
 A parameter that can hold a procedure to override how a browser is

net-lib/net/sendurl.rkt

@@ -3,10 +3,16 @@
 
 #lang racket/base
 
-(require racket/system racket/file racket/promise racket/port)
+(require racket/system racket/file racket/promise racket/port
+         racket/contract)
 
-(provide send-url send-url/file send-url/contents send-url/mac
-         unix-browser-list browser-preference? external-browser)
+(provide send-url send-url/file send-url/contents
+         unix-browser-list browser-preference? external-browser
+         (contract-out
+          [send-url/mac
+           (->* (string?) (#:browser string?)
+                #:pre (equal? (system-type) 'macosx)
+                void?)]))
 
 (define separate-by-default?
   ;; internal configuration, 'browser-default lets some browsers decide