add defines (define*)

from syntax-objects/Summer2021#7
cc @Fictitious-Rotor

defines/defines-test.rkt

@@ -0,0 +1,12 @@
+#lang racket/base
+(module+ test
+  (require rackunit syntax-parse-example/defines/defines)
+
+  (test-case "quot/rem"
+    (defines
+      [x 4]
+      [y 18]
+      [(quot rem) (quotient/remainder x y)])
+    (check-equal? quot 0)
+    (check-equal? rem 4))
+)

defines/defines.rkt

@@ -0,0 +1,10 @@
+#lang racket
+(provide defines)
+(require syntax/parse/define)
+
+(define-syntax-parser defines
+  [(_ (~or [id:id expr:expr]
+           [(idv:id ...+) expr:expr]) ...+)
+   #'(begin
+       (~? (define id expr)
+           (define-values (idv ...) expr)) ...)])

defines/defines.scrbl

@@ -0,0 +1,36 @@
+#lang syntax-parse-example
+@require[
+  (for-label racket/base syntax/parse syntax-parse-example/defines/defines)]
+
+@(define defines-eval
+   (make-base-eval '(require syntax-parse-example/defines/defines)))
+
+@title{@tt{defines}}
+@stxbee2021["Fictitious-Rotor" 7]
+
+@; =============================================================================
+
+@defmodule[syntax-parse-example/defines/defines]{}
+
+@defform[(defines expr ...)]{
+  Make a sequence of definitions --- similar to @racket[let*].
+
+  Definitions are automatically dispatched either to @racket[define] or @racket[define-values]
+  depending on the manner in which identifiers are supplied.
+
+  @examples[#:eval defines-eval
+    (defines
+      [x 4]
+      [y 18]
+      [(quot rem) (quotient/remainder x y)])
+    quot
+    rem
+  ]
+
+  The macro uses the @racket[~?] fallthrough syntax to choose between
+  @racket[define] and @racket[define-values].
+
+  @racketfile{defines.rkt}
+
+  @; TODO add description here
+}

index.scrbl

@@ -16,6 +16,7 @@
 
 @; =============================================================================
 
+@include-example{defines}
 @include-example{first-class-or}
 @include-example{optional-assert}
 @include-example{cross-macro-communication}