Implementing truncate-stream.

* configure: Test for ftruncate and chsize.

* stream.c (unimpl_truncate): New static function.
(fill_stream_ops): Default the truncate operation to unimpl_truncate.
(null_ops): Initialize truncate to unimpl_truncate.
(stdio_truncate): New static function.
(stdio_ops, tail_ops): Initialize truncate to stdio_truncate.
(pipe_ops, dir_ops, string_ops, byte_in_ops, string_out_ops,
strlist_out_ops, cat_stream_ops): Initialize truncate to null,
so it gets defaulted by fill_stream_ops.
(truncate_stream): New function.
(stream_init): Register truncate-stream intrinsic.

* stream.h (struct strm_ops): New member, truncate.
(strm_ops_init): New truncate argument added to macro.
(truncate_stream): Declared.

*syslog.c (syslog_strm_ops): Initialize truncate to null.

* txr.1: Documented.

1 files changed, 15 insertions, 0 deletions

diff --git a/txr.1 b/txr.1
index 32577e58..899b3c69 100644
--- a/txr.1
+++ b/txr.1
@@ -31010,6 +31010,21 @@ and the previous position wasn't zero, then the position is decremented by one.
 On failure, it throws an exception of type
 .codn stream-error .
 
+.coNP Function @ truncate-stream
+.synb
+.mets (truncate-stream < stream << length )
+.syne
+.desc
+The
+.code truncate-stream
+causes the length of the underlying file associated with
+.meta stream
+to be set to
+.meta length
+bytes.
+
+The stream must be a file stream, and must be open for writing.
+
 .coNP Functions @ stream-get-prop and @ stream-set-prop
 .synb
 .mets (stream-get-prop < stream << indicator )