Move docs for syntax/transformer from unstable-doc.

pkgs/racket-doc/syntax/scribblings/transformer-helpers.scrbl

@@ -10,3 +10,4 @@
 @include-section["struct.scrbl"]
 @include-section["path-spec.scrbl"]
 @include-section["template.scrbl"]
+@include-section["transformer.scrbl"]

pkgs/racket-doc/syntax/scribblings/transformer.scrbl

@@ -0,0 +1,39 @@
+#lang scribble/doc
+@(require "common.rkt" scribble/eval (for-label syntax/transformer))
+
+@(define the-eval (make-base-eval))
+@(the-eval '(require syntax/transformer (for-syntax racket/base syntax/transformer)))
+
+@title[#:tag "syntax/transformer"]{Creating Macro Transformers}
+
+@defmodule[syntax/transformer]
+
+@defproc[(make-variable-like-transformer [reference-stx syntax?]
+                                         [setter-stx (or/c syntax? #f) #f])
+         set!-transformer?]{
+
+Creates a transformer that replaces references to the macro identifier
+with @racket[reference-stx]. Uses of the macro in operator position
+are interpreted as an application with @racket[reference-stx] as the
+function and the arguments as given.
+
+If the macro identifier is used as the target of a @racket[set!] form,
+then the @racket[set!] form expands into the application of
+@racket[setter-stx] to the @racket[set!] expression's right-hand side,
+if @racket[setter-stx] is syntax; otherwise, the identifier is
+considered immutable and a syntax error is raised.
+
+@examples[#:eval the-eval
+(define the-box (box add1))
+(define-syntax op
+  (make-variable-like-transformer
+   #'(unbox the-box)
+   #'(lambda (v) (set-box! the-box v))))
+(op 5)
+(set! op 0)
+op
+]
+
+}
+
+@close-eval[the-eval]