From 4f32b4b14f5986447dc3b732b101916412c91d22 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Mon, 17 Jun 2019 07:24:00 -0700
Subject: buffers: sub-buf becomes accessor.

* lisplib.c (ffi_set_entries): Register autoload for sub-buf
symbol.

* share/txr/stdlib/ffi.tl (sub-buf): Syntactic place
defined via defset.

* txr.1: Updated sub-buf documentation.
---
 lisplib.c               |  2 +-
 share/txr/stdlib/ffi.tl |  3 +++
 txr.1                   | 18 +++++++++++++++++-
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/lisplib.c b/lisplib.c
index d2d82b84..45d24eb9 100644
--- a/lisplib.c
+++ b/lisplib.c
@@ -620,7 +620,7 @@ static val ffi_set_entries(val dlt, val fun)
     lit("deffi-sym"), lit("deffi-var"), lit("typedef"), lit("sizeof"),
     lit("alignof"), lit("offsetof"), lit("arraysize"), lit("elemsize"),
     lit("elemtype"), lit("ffi"), lit("carray-ref"), lit("carray-sub"),
-    lit("znew"),
+    lit("sub-buf"), lit("znew"),
     nil
   };
   set_dlt_entries(dlt, name, fun);
diff --git a/share/txr/stdlib/ffi.tl b/share/txr/stdlib/ffi.tl
index 6bbd43a9..0bf111c0 100644
--- a/share/txr/stdlib/ffi.tl
+++ b/share/txr/stdlib/ffi.tl
@@ -148,6 +148,9 @@
 (defset carray-sub (carray : (from 0) (to t)) items
   ^(progn (carray-replace ,carray ,items ,from ,to) ,items))
 
+(defset sub-buf (buf : (from 0) (to t)) items
+  ^(progn (replace-buf ,buf ,items ,from ,to) ,items))
+
 (defmacro znew (type . pairs)
   (if (oddp (length pairs))
     (throwf 'eval-error "~s: slot initform arguments must occur pairwise"
diff --git a/txr.1 b/txr.1
index 7d1f534e..1147ded8 100644
--- a/txr.1
+++ b/txr.1
@@ -59655,9 +59655,10 @@ which has the same length and contents, and compares
 to
 .metn buf .
 
-.coNP Function @ sub-buf
+.coNP Accessor @ sub-buf
 .synb
 .mets (sub-buf < buf >> [ from <> [ to ]])
+.mets (set (sub-buf < buf >> [ from <> [ to ]]) << new-val )
 .syne
 .desc
 The
@@ -59668,6 +59669,21 @@ function, except that the first argument must be a buffer.
 
 The extracted sub-range of a buffer is itself a buffer object.
 
+If
+.code sub-buf
+is used as a syntactic place, the argument expressions
+.metn buf ,
+.metn from ,
+.meta to
+and
+.meta new-val
+are evaluated just once. The prior value, if required, is accessed by calling
+.code buf-sub
+and
+.meta new-val
+is then stored via
+.codn replace-buf .
+
 .coNP Function @ replace-buf
 .synb
 .mets (replace-buf < buf < item-sequence >> [ from <> [ to ]])
-- 
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