Added a /dev/null-like output port to unstable.

collects/meta/props

@@ -1802,6 +1802,7 @@ path/s is either such a string or a list of them.
 "collects/tests/units/test-unit.rktl" drdr:command-line (racket "-f" *)
 "collects/tests/unstable/byte-counting-port.rkt" responsible (jay)
 "collects/tests/unstable/generics.rkt" responsible (jay)
+"collects/tests/unstable/port.rkt" responsible (stamourv)
 "collects/tests/unstable/srcloc.rktl" responsible (cce) drdr:command-line (racket "-f" *)
 "collects/tests/utils" responsible (unknown)
 "collects/tests/utils/gui.rkt" drdr:command-line (gracket-text "-t" *)
@@ -1848,12 +1849,14 @@ path/s is either such a string or a list of them.
 "collects/unstable/match.rkt" responsible (samth)
 "collects/unstable/mutated-vars.rkt" responsible (samth)
 "collects/unstable/poly-c.rkt" responsible (samth)
+"collects/unstable/port.rkt" responsible (stamourv)
 "collects/unstable/scribblings/byte-counting-port.scrbl" responsible (jay)
 "collects/unstable/scribblings/debug.scrbl" responsible (samth)
 "collects/unstable/scribblings/hash.scrbl" responsible (samth)
 "collects/unstable/scribblings/match.scrbl" responsible (samth)
 "collects/unstable/scribblings/mutated-vars.scrbl" responsible (samth)
 "collects/unstable/scribblings/poly-c.scrbl" responsible (samth)
+"collects/unstable/scribblings/port.scrbl" responsible (stamourv)
 "collects/unstable/scribblings/sequence.scrbl" responsible (samth)
 "collects/unstable/scribblings/utils.rkt" responsible (samth)
 "collects/unstable/sequence.rkt" responsible (samth)

collects/tests/unstable/port.rkt

@@ -0,0 +1,23 @@
+#lang racket
+
+(require unstable/port
+         test-engine/scheme-tests)
+
+(check-expect (port? null-output-port)
+              #t)
+
+(check-expect (with-output-to-string
+                (lambda ()
+                  (parameterize ([current-output-port null-output-port])
+                    (display "can't see me"))))
+              "")
+
+(check-expect (with-output-to-string
+                (lambda ()
+                  (display "now you see me")
+                  (parameterize ([current-output-port null-output-port])
+                    (display "now you don't"))
+                  (display "you can see me again")))
+              "now you see meyou can see me again")
+
+(test)

collects/unstable/port.rkt

@@ -0,0 +1,18 @@
+#lang racket/base
+
+(provide null-output-port)
+
+;; taken from section 12.1.9 of the reference
+;; -- stamourv
+(define null-output-port
+  (make-output-port
+   'null
+   always-evt
+   (lambda (s start end non-block? breakable?) (- end start))
+   void
+   (lambda (special non-block? breakable?) #t)
+   (lambda (s start end) (wrap-evt
+                          always-evt
+                          (lambda (x)
+                            (- end start))))
+   (lambda (special) always-evt)))

collects/unstable/scribblings/port.scrbl

@@ -0,0 +1,16 @@
+#lang scribble/doc
+@(require scribble/base
+          scribble/manual
+          "utils.rkt"
+          (for-label unstable/port
+                     racket/base))
+
+@title[#:tag "port"]{Port}
+
+@defmodule[unstable/port]
+
+@unstable[@author+email["Vincent St-Amour" "stamourv@ccs.neu.edu"]]
+
+@defthing[null-output-port output-port?]{
+ Output port that discards everything written to it.
+}

collects/unstable/scribblings/unstable.scrbl

@@ -90,6 +90,7 @@ Keep documentation and tests up to date.
 @include-section["sequence.scrbl"]
 @include-section["hash.scrbl"]
 @include-section["match.scrbl"]
+@include-section["port.scrbl"]
 @include-section["skip-list.scrbl"]
 @include-section["interval-map.scrbl"]
 @include-section["generics.scrbl"]