Support for pushing back bytes and characters into streams.

* stream.c (null_ops, stdio_ops, tail_ops, pipe_ops,
string_in_ops, byte_in_ops, string_out_ops, strlist_out_ops,
dir_ops, cat_stream_ops): Structure definition updated
with new initializers for two new virtuals.
(stdio_handle): New member, unget_c.
(snarf_line, stdio_get_char): Handle pushed-back character in
h->unget_c.
(stdio_unget_char, stdio_unget_byte, string_in_unget_char,
byte_in_unget_byte): New static functions.
(make_stdio_stream_common): Initialize unget_c member.
(unget_char, unget_byte): New functions.

* stream.h (struct strm_ops): New virtuals: unget_char and unget_byte.
(unget_char, unget_byte): New functions declared.

* syslog.c (syslog_strm_ops): Two new initializers.

* eval.c (eval_init): Registered unget_char and unget_byte as
intrinsics.

* txr.1: Documented.

1 files changed, 2 insertions, 0 deletions

diff --git a/syslog.c b/syslog.c
index 39581d34..f544c110 100644
--- a/syslog.c
+++ b/syslog.c
@@ -219,6 +219,8 @@ static struct strm_ops syslog_strm_ops = {
   0, /* get_line */
   0, /* get_char */
   0, /* get_byte */
+  0, /* unget_char */
+  0, /* unget_byte */
   0, /* close */
   0, /* flush */
   0, /* seek */