From 5afa815c9cd4550bf93181bc0ed0134aa83dfc5d Mon Sep 17 00:00:00 2001
From: Andy Wingo <wingo@pobox.com>
Date: Fri, 15 Jan 2010 22:24:31 +0100
Subject: [PATCH] add reader option for parsing [] as ().

* libguile/private-options.h:
* libguile/read.c (scm_read_opts, SCM_SQUARE_BRACKETS_P): Add an option
  for treating [ and ] as parentheses, on by default. Note that this
  makes them delimiters also, so [ and ] cannot appear in a symbol name,
  with this read option on.
  (scm_read_sexp): If we start with [, we end with ].
  (scm_read_expression): Add case for [.
---
 libguile/private-options.h |  3 ++-
 libguile/read.c            | 11 +++++++++--
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/libguile/private-options.h b/libguile/private-options.h
index 40d40fbd7..f027b72e6 100644
--- a/libguile/private-options.h
+++ b/libguile/private-options.h
@@ -4,7 +4,7 @@
  * We put this in a private header, since layout of data structures
  * is an implementation detail that we want to hide.
  * 
- * Copyright (C) 2007, 2009 Free Software Foundation, Inc.
+ * Copyright (C) 2007, 2009, 2010 Free Software Foundation, Inc.
  * 
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public License
@@ -96,6 +96,7 @@ SCM_API scm_t_option scm_read_opts[];
 #define SCM_ESCAPED_PARENS_P   scm_read_opts[5].val
 #endif
 #define SCM_R6RS_ESCAPES_P     scm_read_opts[6].val
+#define SCM_SQUARE_BRACKETS_P  scm_read_opts[7].val
 
 #if SCM_ENABLE_ELISP
 #define SCM_N_READ_OPTIONS 7
diff --git a/libguile/read.c b/libguile/read.c
index edcb6ed1d..a6fa4e95b 100644
--- a/libguile/read.c
+++ b/libguile/read.c
@@ -78,6 +78,8 @@ scm_t_option scm_read_opts[] = {
 #endif
   { SCM_OPTION_BOOLEAN, "r6rs-hex-escapes", 0,
     "Use R6RS variable-length character and string hex escapes."},
+  { SCM_OPTION_BOOLEAN, "square-brackets", 1,
+    "Treat `[' and `]' as parentheses, for R6RS compatibility."},
   { 0, },
 };
 
@@ -173,7 +175,8 @@ static SCM *scm_read_hash_procedures;
    structure'').  */
 #define CHAR_IS_R5RS_DELIMITER(c)				\
   (CHAR_IS_BLANK (c)						\
-   || (c == ')') || (c == '(') || (c == ';') || (c == '"'))
+   || (c == ')') || (c == '(') || (c == ';') || (c == '"')      \
+   || (SCM_SQUARE_BRACKETS_P && ((c == '[') || (c == ']'))))
 
 #define CHAR_IS_DELIMITER  CHAR_IS_R5RS_DELIMITER
 
@@ -332,7 +335,7 @@ scm_read_sexp (scm_t_wchar chr, SCM port)
   register SCM tmp;
   register SCM tl, ans = SCM_EOL;
   SCM tl2 = SCM_EOL, ans2 = SCM_EOL, copy = SCM_BOOL_F;
-  static const int terminating_char = ')';
+  const int terminating_char = ((chr == '[') ? ']' : ')');
 
   /* Need to capture line and column numbers here. */
   long line = SCM_LINUM (port);
@@ -1251,6 +1254,10 @@ scm_read_expression (SCM port)
 	case ';':
 	  (void) scm_read_semicolon_comment (chr, port);
 	  break;
+	case '[':
+          if (!SCM_SQUARE_BRACKETS_P)
+            return (scm_read_mixed_case_symbol (chr, port));
+          /* otherwise fall through */
 	case '(':
 	  return (scm_read_sexp (chr, port));
 	case '"':