* match.c (dest_bind): Remove the restriction of not allowing

@(expr ...) and @var on the left side of a bind. This
is useful, and necessary for @(line @(lisp expr)) to work:
matching computed line numbers and character positions.

* txr.1: Document use of Lisp on left hand side of bind,
that there is a restriction on the left hand side of a set,
and that Lisp can be used in a line or chr directive for
computed matches.

3 files changed, 81 insertions, 2 deletions

diff --git a/ChangeLog b/ChangeLog
index 5d876612..6453947e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,17 @@
 2014-10-17  Kaz Kylheku  <kaz@kylheku.com>
 
+	* match.c (dest_bind): Remove the restriction of not allowing
+	@(expr ...) and @var on the left side of a bind. This
+	is useful, and necessary for @(line @(lisp expr)) to work:
+	matching computed line numbers and character positions.
+
+	* txr.1: Document use of Lisp on left hand side of bind,
+	that there is a restriction on the left hand side of a set,
+	and that Lisp can be used in a line or chr directive for
+	computed matches.
+
+2014-10-17  Kaz Kylheku  <kaz@kylheku.com>
+
 	* HACKING: New section Type Safety.
 	Table of contents regenerated with line numbers.
 
diff --git a/match.c b/match.c
index 95328b32..9e699646 100644
--- a/match.c
+++ b/match.c
@@ -296,15 +296,27 @@ static val dest_bind(val spec, val bindings, val pattern,
     }
   } else if (consp(pattern)) {
     val piter = pattern, viter = value;
+    val lisp_evaled = nil;
+    val ret;
 
     if (first(pattern) == var_s) {
-      sem_error(spec, lit("metavariable @~a syntax cannot be used here"), second(pattern), nao);
+      uw_env_begin;
+      uw_set_match_context(cons(spec, bindings));
+      ret = eval(second(pattern), make_env(bindings, nil, nil), pattern);
+      lisp_evaled = t;
+      uw_env_end;
     }
 
     if (first(pattern) == expr_s) {
-      sem_error(spec, lit("the @~s syntax cannot be used here"), rest(pattern), nao);
+      uw_env_begin;
+      uw_set_match_context(cons(spec, bindings));
+      ret = eval(rest(pattern), make_env(bindings, nil, nil), pattern);
+      lisp_evaled = t;
+      uw_env_end;
     }
 
+    if (lisp_evaled)
+      return if3(tree_find(value, ret, swap_12_21(testfun)), bindings, t);
 
     while (consp(piter) && consp(viter))
     {
diff --git a/txr.1 b/txr.1
index 4541c485..006d3b0a 100644
--- a/txr.1
+++ b/txr.1
@@ -3678,6 +3678,19 @@ takes the entire line of input:
   @(chr 0)@(chr 0)@x
 .cble
 
+The argument of
+.code line
+or
+.code chr
+may be a
+.codn @ -delimited
+Lisp expression. This is useful for matching computed lines or
+character positions:
+
+.cblk
+  @(line @(+ a (* b c)))
+.cble
+
 .dirs some all none maybe cases choose
 
 These directives, called the parallel directives, combine multiple subqueries,
@@ -5351,6 +5364,33 @@ matches
 .str c
 if these are upcased.
 
+.coNP Lisp forms in the @ bind directive
+
+\*(TL forms, introduced by
+.code @
+may be used on either side of
+.codn bind .
+
+
+Example:
+
+.cblk
+  @(bind a @(+ 2 2))
+  @(bind @(+ 2 2) @(* 2 2))
+.cble
+
+Here,
+.code a
+is bound to the integer
+.codn 4 .
+The second
+.code bind
+then succeeds because the forms
+.code (+ 2 2)
+and
+.code (* 2 2)
+produce equal values.
+
 .dir set
 
 The
@@ -5420,6 +5460,21 @@ binds to
   @(set (A B . C) D)
 .cble
 
+Note that
+.code set
+does not support a \*(TL expression on the left side, so the following
+are invalid syntax:
+
+.cblk
+  @(set @(+ 1 1) @(* 2 2))
+  @(set @b @(list "a"))
+.cble
+
+The second one is erroneous even though there is a variable on the left.
+Because it is preceded by the
+.code @
+escape, it is a Lisp variable, and not a pattern variable.
+
 .dir rebind
 
 The