Improvement in place macros.

Expansion of places now gives priority to place macros.
Moreover, it iterates over place macro and ordinary macro
expansion.

* share/txr/stdlib/place.tl (sys:trigger-load): Removed.
(sys:pl-expand): Rewritten.

* txr.1: Documented.

1 files changed, 25 insertions, 3 deletions

diff --git a/txr.1 b/txr.1
index 9b33de81..b3dd7451 100644
--- a/txr.1
+++ b/txr.1
@@ -24681,9 +24681,31 @@ has the same syntax as
 It specifies a macro transformation for a compound form which has the
 .meta name
 symbol in its leftmost position.
-This macro expansion is applied when such a form is used as a place.
-It is applied after all other expansions, and no other macro-expansions
-are applied afterward.
+
+Forms which are used as syntactic places are subject to a modified
+macro-expansion algorithm. If a place macro applies to a place, then it is
+expanded, otherwise it is taken as-is. Then the place is expanded as a ordinary
+macro (possibly a symbol macro). Then the process is repeated from the
+beginning, as necessary.  Thus, the output of the ordinary macro expansion may
+potentially be, again, a place macro. Place macros can expand to other place
+macros or ordinary macros and vice versa.
+
+Place macro expansion doesn't use an environment; place macros are in a single
+global namespace, special to place macros. There are no lexically scoped place
+macros. Such an effect can be achieved by having a place macro expand to
+an a form which is the target of a global or local macro, as necessary.
+
+The
+.code define-place-macro
+form does not cause
+.meta name
+to become
+.code fboundp
+or
+.codn boundp .
+
+There can exist both an ordinary macro and a place macro of the same name;
+moreover, this is potentially useful.
 
 .TP* "Example:"