From 632deb8aa26bec72d3b5b9d920551239a3e5f559 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Wed, 12 Aug 2015 07:19:43 -0700
Subject: Revision to .. syntax.

* parser.y (r_exprs, n_expr): Move the DOTDOT syntactic sugar rule from
r_exprs to n_expr, where it is much simpler. This also means that the
a..b syntax is now an expression by itself; it need not be enclosed in
a list.  The DOTDOT operator is made right associative; or rather
its existing %right declaration is now activated.

* txr.1: Remove documentation stating that the .. notation must
be used in a list, and not in the dotted position of an improper
list. Document the behavior in the dotted position, and document
right associativity.
---
 parser.y | 13 +++----------
 txr.1    | 36 +++++++++++++++---------------------
 2 files changed, 18 insertions(+), 31 deletions(-)

diff --git a/parser.y b/parser.y
index 4db7ae90..641422f3 100644
--- a/parser.y
+++ b/parser.y
@@ -763,16 +763,6 @@ r_exprs : n_expr                { val exprs = cons($1, nil);
                                   misplaced_consing_dot_check(scnr, term_atom_cons);
                                   rplaca(term_atom_cons, $3);
                                   $$ = $1; }
-        | r_exprs DOTDOT n_expr { uses_or2;
-                                  val term_atom_cons = $1;
-                                  val exprs = cdr($1);
-                                  misplaced_consing_dot_check(scnr, term_atom_cons);
-                                  rplacd(term_atom_cons,
-                                         rlcp(cons(list(cons_s, car(exprs),
-                                                        $3, nao),
-                                                   cdr(exprs)),
-                                              or2($3, exprs)));
-                                  $$ = term_atom_cons; }
         | WSPLICE wordslit      { $$ = cons(nil, nreverse(rl($2, num($1))));
                                   rlcp($$, cdr($$)); }
         | r_exprs WSPLICE
@@ -816,6 +806,9 @@ n_expr : SYMTOK                 { $$ = symhlpr($1, t); }
                                           num(parser->lineno)); }
        | SPLICE n_expr          { $$ = rl(rlcp(list(sys_splice_s, $2, nao), $2),
                                           num(parser->lineno)); }
+       | n_expr DOTDOT n_expr   { uses_or2;
+                                  $$ = rlcp(list(cons_s, $1, $3, nao),
+                                            or2($1, $3)); }
        | n_expr '.' n_expr      { uses_or2;
                                   if (consp($3) && car($3) == qref_s) {
                                     rplacd($3, rlcp(cons($1, cdr($3)), $1));
diff --git a/txr.1 b/txr.1
index 2954fc4b..6ef3db2d 100644
--- a/txr.1
+++ b/txr.1
@@ -9509,28 +9509,22 @@ computes a sublist of
 consisting of
 elements 1 through 2 (counting from zero).
 
-Restrictions:
-
-The notation must be enclosed in a list. For instance
-.code a..b
-is not, by itself, an
-expression, but
-.code (a..b)
-is. This is important if Lisp data is being parsed from
-a string or stream using the read function. If the data
-.str "a..b"
-is parsed, the symbol
-.code a
-will be extracted, leaving
-.strn ..a ,
-which, if parsed,
-produces a syntax error since it consists of a "dotdot" token followed by
-a symbol, which is not valid syntax.
-
-The notation cannot occur in the dot position; that is, the syntax
+Note that if this notation is used in the dot position of an improper
+list, the transformation still applies. That is, the syntax
 .code (a . b .. c)
-is invalid. The dotdot operator can only be used between the non-dot-position
-elements of a list.
+is valid and produces the object
+.code (a . (cons b c))
+which is another way of writing
+.codn (a cons b c) .
+
+The notation's
+.code ..
+operator associates right to left, so that
+.code a..b..c
+denotes
+.code (cons a (cons b c))
+or
+.codn (a b . c) .
 
 .NP* The DWIM Brackets
 \*(TL has a square bracket notation. The syntax
-- 
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