stream: stream_reset

We can reuse the same stream by resetting it.  We don't delete the
cached data.

include/alisp/stream.h

@@ -56,6 +56,7 @@ stream_err_t stream_init_pipe(stream_t *, const char *, FILE *);
 // NOTE: stream_init_file will attempt to read all content from the FILE
 // descriptor.  Use with caution.
 stream_err_t stream_init_file(stream_t *, const char *, FILE *);
+void stream_reset(stream_t *);
 void stream_stop(stream_t *);
 
 // End of Content (i.e. we've consumed all cached content/file)

src/stream.c

@@ -100,6 +100,13 @@ stream_err_t stream_init_file(stream_t *stream, const char *name, FILE *pipe)
   return STREAM_ERR_OK;
 }
 
+void stream_reset(stream_t *stream)
+{
+  if (!stream)
+    return;
+  stream->position = 0;
+}
+
 void stream_stop(stream_t *stream)
 {
   if (!stream)