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, 4 insertions, 0 deletions

diff --git a/stream.h b/stream.h
index e2ea714d..6a76d6b8 100644
--- a/stream.h
+++ b/stream.h
@@ -38,6 +38,8 @@ struct strm_ops {
   val (*get_line)(val);
   val (*get_char)(val);
   val (*get_byte)(val);
+  val (*unget_char)(val, val);
+  val (*unget_byte)(val, int);
   val (*close)(val, val);
   val (*flush)(val);
   val (*seek)(val, cnum, enum strm_whence);
@@ -78,6 +80,8 @@ val close_stream(val stream, val throw_on_error);
 val get_line(val);
 val get_char(val);
 val get_byte(val);
+val unget_char(val ch, val stream);
+val unget_byte(val byte, val stream);
 val vformat(val stream, val string, va_list);
 val vformat_to_string(val string, va_list);
 val format(val stream, val string, ...);