From 87a5ee4cc1d0d40af658c015562c0f492c1035e5 Mon Sep 17 00:00:00 2001
From: Alexis King <lexi.lambda@gmail.com>
Date: Thu, 17 May 2018 13:32:46 -0500
Subject: [PATCH] Make syntax-local-introduce work in syntax/parse pattern
 expanders

---
 .../racket-doc/syntax/scribblings/parse/patterns.scrbl |  5 +++--
 racket/collects/syntax/parse/private/rep.rkt           | 10 +++-------
 racket/collects/syntax/parse/private/residual-ct.rkt   |  8 +-------
 3 files changed, 7 insertions(+), 16 deletions(-)

diff --git a/pkgs/racket-doc/syntax/scribblings/parse/patterns.scrbl b/pkgs/racket-doc/syntax/scribblings/parse/patterns.scrbl
index 3908793c9e..c2f73a1581 100644
--- a/pkgs/racket-doc/syntax/scribblings/parse/patterns.scrbl
+++ b/pkgs/racket-doc/syntax/scribblings/parse/patterns.scrbl
@@ -1181,7 +1181,8 @@ Returns @racket[#t] if @racket[v] is a @tech{pattern expander},
 
 @defproc[(syntax-local-syntax-parse-pattern-introduce [stx syntax?]) syntax?]{
 
-Like @racket[syntax-local-introduce], but for @tech{pattern expanders}.
-}
+For backward compatibility only; equivalent to @racket[syntax-local-introduce].
+
+@history[#:changed "6.90.0.29" @elem{Made equivalent to @racket[syntax-local-introduce].}]}
 
 @(close-eval the-eval)
diff --git a/racket/collects/syntax/parse/private/rep.rkt b/racket/collects/syntax/parse/private/rep.rkt
index 228b1762a7..490371b5a5 100644
--- a/racket/collects/syntax/parse/private/rep.rkt
+++ b/racket/collects/syntax/parse/private/rep.rkt
@@ -7,6 +7,7 @@
          racket/contract/base
          "make.rkt"
          "minimatch.rkt"
+         syntax/apply-transformer
          syntax/private/id-table
          syntax/stx
          syntax/keyword
@@ -616,13 +617,8 @@
 
 ;; expand-pattern : pattern-expander Syntax -> Syntax
 (define (expand-pattern pe stx)
-  (let* ([proc (pattern-expander-proc pe)]
-         [introducer (make-syntax-introducer)]
-         [mstx (introducer (syntax-local-introduce stx))]
-         [mresult (parameterize ([current-syntax-parse-pattern-introducer introducer])
-                    (proc mstx))]
-         [result (syntax-local-introduce (introducer mresult))])
-    result))
+  (let ([proc (pattern-expander-proc pe)])
+    (local-apply-transformer proc stx 'expression)))
 
 ;; parse-ellipsis-head-pattern : stx DeclEnv -> (listof EllipsisHeadPattern)
 (define (parse-ellipsis-head-pattern stx decls)
diff --git a/racket/collects/syntax/parse/private/residual-ct.rkt b/racket/collects/syntax/parse/private/residual-ct.rkt
index 9d9924b353..53ccd2c6fc 100644
--- a/racket/collects/syntax/parse/private/residual-ct.rkt
+++ b/racket/collects/syntax/parse/private/residual-ct.rkt
@@ -19,7 +19,6 @@
          prop:pattern-expander
          pattern-expander?
          pattern-expander-proc
-         current-syntax-parse-pattern-introducer
          syntax-local-syntax-parse-pattern-introduce)
 
 (define-logger syntax-parse)
@@ -94,10 +93,5 @@ An EH-alternative is
   (define get-proc (get-proc-getter pat-expander))
   (get-proc pat-expander))
 
-(define current-syntax-parse-pattern-introducer
-  (make-parameter
-   (lambda (stx)
-     (error 'syntax-local-syntax-parse-pattern-introduce "not expanding syntax-parse pattern"))))
-
 (define (syntax-local-syntax-parse-pattern-introduce stx)
-  ((current-syntax-parse-pattern-introducer) stx))
+  (syntax-local-introduce stx))