From 2a001c9577b9364cc866638f94abd51ddb020b4f Mon Sep 17 00:00:00 2001
From: Jeff Bezanson <jeff.bezanson@gmail.com>
Date: Wed, 17 Jan 2018 14:16:40 -0500
Subject: [PATCH] disallow `begin` inside indexing

part of #23354, #25458
---
 NEWS.md              | 3 +++
 src/julia-parser.scm | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/NEWS.md b/NEWS.md
index 1d8be550428a8..1f9ff6c420a03 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -184,6 +184,9 @@ Language changes
   * `=>` now has its own precedence level, giving it strictly higher precedence than
     `=` and `,` ([#25391]).
 
+  * `begin` is disallowed inside indexing expressions, in order to enable the syntax
+    `a[begin]` (for selecting the first element) in the future ([#23354]).
+
   * Underscores for `_italics_` and `__bold__` are now supported by the Base Markdown
     parser. ([#25564])
 
diff --git a/src/julia-parser.scm b/src/julia-parser.scm
index 80ab7f33fa933..4d4d9f616ff66 100644
--- a/src/julia-parser.scm
+++ b/src/julia-parser.scm
@@ -1318,6 +1318,8 @@
 
 ;; parse expressions or blocks introduced by syntactic reserved words
 (define (parse-resword s word)
+  (if (and (eq? word 'begin) end-symbol)
+      (parser-depwarn s "\"begin\" inside indexing expression" ""))
   (with-bindings
    ((expect-end-current-line (input-port-line (ts:port s))))
    (with-normal-context