Default the length argument of truncate-stream.

* stream.c (truncate_stream): If the len argument is missing,
default to the current position, obtained by using the seek
operation.
(stream_init): Fix up registration of truncate-stream for one
optional argument.

* txr.1: Documentation of truncate-stream updated.

1 files changed, 16 insertions, 1 deletions

diff --git a/txr.1 b/txr.1
index b228334f..911143dd 100644
--- a/txr.1
+++ b/txr.1
@@ -42537,7 +42537,7 @@ On failure, it throws an exception of type
 
 .coNP Function @ truncate-stream
 .synb
-.mets (truncate-stream < stream << length )
+.mets (truncate-stream < stream <> [ length ])
 .syne
 .desc
 The
@@ -42550,6 +42550,21 @@ bytes.
 
 The stream must be a file stream, and must be open for writing.
 
+If
+.meta length
+is omitted, then it defaults to the current position, retrieved
+as if by invoking the
+.code seek-stream
+with an
+.meta offset
+argument of zero and
+.meta whence
+argument of
+.codn :from-current .
+Hence, after the
+.code truncate-stream
+operation, that position is one byte past the end of the file.
+
 .coNP Functions @ stream-get-prop and @ stream-set-prop
 .synb
 .mets (stream-get-prop < stream << indicator )