Made it possible not to give a filename

scrbl/rkdt.scrbl

@@ -2,6 +2,7 @@
 
 @(require (for-label racket/base
                      racket/class
+                     racket/contract
                      "../main.rkt"))
 
 @title{rackedit}
@@ -11,12 +12,12 @@
 
 @tt{rackedit} provides a small editor window based on Racket's GUI framework.
 It is intended for situations where a program, DrRacket interaction, or command
-line session needs to open a file in a simple Racket editor without starting a
-separate full editor application.
+line session needs a simple Racket editor, optionally for a specific file, without
+starting a separate full editor application.
 
 @section{Opening an editor}
 
-@defproc[(rkdt [filename path-string?]
+@defproc[(rkdt [filename (or/c path-string? #f) #f]
                [#:wait? wait? boolean? #f]
                [#:width width exact-positive-integer? 900]
                [#:height height exact-positive-integer? 650]
@@ -26,11 +27,14 @@ separate full editor application.
                             (λ (call-time frame) #t)])
          void?]{
 
-@bold{Purpose.} Opens an editor window for @racket[filename].
+@bold{Purpose.} Opens an editor window. When @racket[filename] is a path or
+string, that file is opened. When @racket[filename] is @racket[#f], which is the
+default, an empty editor is opened.
 
-@bold{Preconditions.} @racket[filename] identifies the file to open.
-@racket[frame-cb] must accept two arguments: a lifecycle symbol and the editor
-frame. The geometry arguments specify valid dimensions and screen coordinates.
+@bold{Preconditions.} When supplied, @racket[filename] identifies the file to
+open. @racket[frame-cb] must accept two arguments: a lifecycle symbol and the
+editor frame. The geometry arguments specify valid dimensions and screen
+coordinates.
 
 @bold{Postconditions.} An editor frame has been created and shown. When
 @racket[wait?] is @racket[#f], @racket[rkdt] returns after the frame has been
@@ -40,7 +44,11 @@ shown and the @racket['after-show] callback has run. When @racket[wait?] is
 @bold{Result.} The procedure returns @racket[(void)]. The editor frame itself is
 made available to @racket[frame-cb] during its lifecycle callbacks.
 
-@bold{Internal workings.} Each open editor receives an internal number. That
+@bold{Internal workings.} A non-false @racket[filename] is converted to a
+string before it is supplied to the Framework editor frame. A false filename is
+passed through as @racket[#f], causing the frame to start without a file.
+
+Each open editor receives an internal number. That
 number is appended to the window title and is used to distinguish stored window
 geometry. Numbers belonging to closed editors are reused. On close, the current
 position and size are stored for that internal number and the current screen
@@ -85,11 +93,17 @@ between @racket['after-show] and @racket['on-close].
 
 @section{Examples}
 
-The simplest use opens a file and returns immediately:
+The simplest use opens an empty editor and returns immediately:
 
 @racketblock[
 (require rackedit)
 
+(rkdt)
+]
+
+Supply a filename to open a file:
+
+@racketblock[
 (rkdt "notes.rkt")
 ]