From f51e7f910d7b77801094d3de0e6917560554f1ac Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Wed, 14 Sep 2016 06:48:35 -0700
Subject: New place-mutating macro: upd.

* lisplib.c (place_set_entries): Add upd to the auto-load
list for place.tl.
* share/txr/stdlib/place.tl (upd): New macro.

* txr.1: Documented.
---
 lisplib.c                 |  2 +-
 share/txr/stdlib/place.tl |  5 +++++
 txr.1                     | 34 ++++++++++++++++++++++++++++++++++
 3 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/lisplib.c b/lisplib.c
index e1b2a9ca..e74c925e 100644
--- a/lisplib.c
+++ b/lisplib.c
@@ -69,7 +69,7 @@ static val place_set_entries(val dlt, val fun)
     lit("with-delete-expander"),
     lit("set"), lit("pset"), lit("zap"), lit("flip"), lit("inc"), lit("dec"),
     lit("push"), lit("pop"), lit("swap"), lit("shift"), lit("rotate"),
-    lit("pushnew"), lit("del"), lit("lset"),
+    lit("pushnew"), lit("del"), lit("lset"), lit("upd"),
     lit("defplace"), lit("define-place-macro"), lit("define-modify-macro"),
     lit("placelet"), lit("placelet*"), lit("define-acessor"),
     lit("with-slots"),
diff --git a/share/txr/stdlib/place.tl b/share/txr/stdlib/place.tl
index d580d91a..61654509 100644
--- a/share/txr/stdlib/place.tl
+++ b/share/txr/stdlib/place.tl
@@ -371,6 +371,11 @@
                            places))
        ,orig)))
 
+(defmacro upd (place . opip-args)
+  (with-gensyms (pl)
+    ^(placelet ((,pl ,place))
+       (set ,pl (call (opip ,*opip-args) ,pl)))))
+
 (defmacro defplace (place-destructuring-args body-sym
                     (getter-sym setter-sym update-body) :
                     ((ssetter-sym clobber-body))
diff --git a/txr.1 b/txr.1
index 615ae663..47a4f0aa 100644
--- a/txr.1
+++ b/txr.1
@@ -11374,6 +11374,14 @@ Sets multiple places to values obtained from successive
 elements of
 .metn sequence .
 
+.meIP (upd < place << opip-arg *)
+Applies an
+.codn opip -style
+operational pipeline to the value of
+.meta place
+and stores the result back into
+.metn place .
+
 .PP
 
 .SS* Namespaces and Environments
@@ -26545,6 +26553,32 @@ form produces the value of
 .meta sequence-expr
 as its result value.
 
+.coNP Macro @ upd
+.synb
+.mets (upd < place << opip-arg *)
+.syne
+.desc
+The
+.code upd
+macro evaluates
+.meta place
+and passes the value as an argument to the operational pipeline
+function formed,
+as if by the
+.code opip
+macro, from the
+.meta opip-arg
+arguments.  The result of this function is then stored back into
+.metn place .
+
+The following equivalence holds, except that place
+.code p
+is evaluated only once:
+
+.cblk
+  (upd p x y z ...)  <-->  (set p (call (opip x y z ...) p))
+.cble
+
 .SS* User-Defined Places and Place Operators
 \*(TL provides a number of place-modifying operators such as
 .codn set ,
-- 
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