compile-file/load: add version to files.

* parser.c (read_file_common): Treat first form in file as a
version number of the form (major minor), where major nad
minor are non-negative integers. If the major number is
greater than zero, reject the file as incompatible.

* share/txr/stdlib/compiler.tl (usr:compile-file): Emit version
number (0 0) as the first item in a compiled file.

2 files changed, 10 insertions, 1 deletions

diff --git a/parser.c b/parser.c
index 081b8137..f39293ee 100644
--- a/parser.c
+++ b/parser.c
@@ -610,6 +610,7 @@ static val read_file_common(val stream, val error_stream, val compiled)
 {
   val error_val = gensym(nil);
   val name = stream_get_prop(stream, name_k);
+  val first = t;
 
   for (;;) {
     val form = lisp_parse(stream, error_stream, error_val, name, colon_k);
@@ -623,7 +624,14 @@ static val read_file_common(val stream, val error_stream, val compiled)
       continue;
     }
 
-    if (compiled) {
+    if (compiled && first) {
+      val major = pop(&form);
+      if (gt(major, zero))
+        uw_throwf(error_s,
+                  lit("cannot load ~s; it was compiled by a newer implementation"),
+                  stream, nao);
+      first = nil;
+    } else if (compiled) {
       val nlevels = pop(&form);
       val nregs = pop(&form);
       val bytecode = pop(&form);
diff --git a/share/txr/stdlib/compiler.tl b/share/txr/stdlib/compiler.tl
index 24fa5c2a..a75b4571 100644
--- a/share/txr/stdlib/compiler.tl
+++ b/share/txr/stdlib/compiler.tl
@@ -1374,6 +1374,7 @@
                             (when *emit*
                               (let ((*print-circle* t))
                                 (prinl flat-vd out-stream))))))))))
+        (prinl '(0 0) out-stream)
         (whilet ((obj (read in-stream *stderr* err-ret))
                  ((neq obj err-ret)))
           (compile-form (sys:expand* obj)))