oop: make struct symbol supertype of all structs.

* lib.c (subtypep): If the supertype is struct, then return t
if the subtype is the name of a struct type.

* txr.1: Update the type graph to show the struct root, adding
a note about it.

1 files changed, 2 insertions, 0 deletions

diff --git a/lib.c b/lib.c
index 06cd37c1..da8e0bf7 100644
--- a/lib.c
+++ b/lib.c
@@ -257,6 +257,8 @@ val subtypep(val sub, val sup)
     return tnil(sub == str_s || sub == lit_s || sub == lstr_s);
   } else if (sup == stream_s) {
     return tnil(sub == stdio_stream_s);
+  } else if (sup == struct_s) {
+    return tnil(find_struct_type(sub));
   } else {
     val sub_struct = find_struct_type(sub);
     val sup_struct = find_struct_type(sup);