From 365fed987251528b61419c24047d13c49c9f7191 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Georges=20Dup=C3=A9ron?= <georges.duperon@gmail.com>
Date: Wed, 28 Sep 2016 23:22:12 +0200
Subject: [PATCH] Added and documented ~as-rest

---
 main.rkt               |  1 +
 private/no-order.rkt   | 18 ++++++++++++++++++
 scribblings/rest.scrbl | 24 +++++++++++++++++++++++-
 3 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/main.rkt b/main.rkt
index eed1d92..000ded0 100644
--- a/main.rkt
+++ b/main.rkt
@@ -34,6 +34,7 @@
          ~try-before
          ~try-after
          ~lift-rest
+         ~as-rest
          ~mixin
          ~post-check
          ~post-fail
diff --git a/private/no-order.rkt b/private/no-order.rkt
index 7cf2abb..8702a4a 100644
--- a/private/no-order.rkt
+++ b/private/no-order.rkt
@@ -43,6 +43,7 @@
          try-order-point<
          try-order-point>
          ~lift-rest
+         ~as-rest
          ~omitable-lifted-rest ;; Private
          (expander-out eh-mixin)) ;; Private
 
@@ -293,6 +294,23 @@
            {~do 'expanded-pats}
            {~bind [clause-present #t]}}]))))
 
+(define-eh-mixin-expander ~as-rest
+  (λ (stx)
+    (syntax-case stx ()
+      [(_ pat ...)
+       (let ()
+         (define/with-syntax clause-present (get-new-clause!))
+         (define/with-syntax clause-seq (get-new-clause!))
+         (define/with-syntax (expanded-pat ...)
+           ;; let the ~post, ~global etc. within pat … be recognized
+           (stx-map expand-all-eh-mixin-expanders #'(pat ...)))
+         (lift-rest! '~lift-rest
+                     #'clause-present
+                     #'({~parse (expanded-pat ...)
+                                #'(clause-seq (... ...))}))
+         #'{~seq clause-seq (... ...)
+                 {~bind [clause-present #t]}})])))
+
 (define-eh-mixin-expander ~lift-rest
   (λ (stx)
     (syntax-case stx ()
diff --git a/scribblings/rest.scrbl b/scribblings/rest.scrbl
index 15d5360..44d99cf 100644
--- a/scribblings/rest.scrbl
+++ b/scribblings/rest.scrbl
@@ -12,7 +12,6 @@
 
 @defform[#:kind "eh-mixin expander"
          {~lift-rest pat}]{
-                           
  Lifts @racket[pat] out of the current mixin, so that it is used as a pattern to
  match the tail of the improper list being matched. It is subject to the
  following restrictions:
@@ -65,3 +64,26 @@
  @item{Post and global operations can be used within the @racket[pat]. This
    combination of features is not thoroughly tested, however. Please report any
    issues you run into.}]}
+
+@defform[#:kind "eh-mixin expander"
+         {~as-rest pat ...}]{
+                             
+ Like @racket[~seq], but the @racket[pat]s are injected as part of the same
+ @racket[~or] as @racket[~lift-rest]. This means that syntax/parse will not
+ throw an error for the following code:
+
+ @examples[#:eval (make-evaluator)
+           (eval:no-prompt
+            (define p2
+              (syntax-parser
+                [(~no-order {~once name:id}
+                            {~once message:str}
+                            (~once (~or {~as-rest val:nat}
+                                        {~seq {~lift-rest val:nat}})))
+                 (syntax->datum
+                  #'(#:name name #:messsage message #:val val))])))
+           (code:line (p2 #'(x 123 "msg"))       (code:comment "matched by ~as-rest"))
+           (code:line (p2 #'(x "msg" 123))       (code:comment "matched by ~as-rest"))
+           (code:line (p2 #'(x "msg" . 456))     (code:comment "matched by ~lift-rest"))
+           (eval:alts (code:line (p2 #'(x "msg" 123 . 456)) (code:comment "can't have both"))
+                      (eval:error (p2 #'(x "msg" 123 . 456))))]}
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