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.

1 files changed, 17 insertions, 1 deletions

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 ]])