Allow super to take an instance as an argument.

* struct.c (super): Detect structure instance
and resolve it to its type. Recursion eliminated in favor of
imperative approach that eliminates redundant checks.

* txr.1: Description of super updated.

2 files changed, 9 insertions, 4 deletions

diff --git a/struct.c b/struct.c
index 9de7d0c5..054b5f09 100644
--- a/struct.c
+++ b/struct.c
@@ -263,8 +263,12 @@ val super(val type)
     val stype = find_struct_type(type);
     if (!stype)
       no_such_struct(lit("super"), type);
-    return super(stype);
-  } else {
+    type = stype;
+  } else if (structp(type)) {
+    type = struct_type(type);
+  }
+
+  {
     struct struct_type *st = coerce(struct struct_type *,
                                     cobj_handle(type, struct_type_s));
     return st->super;
diff --git a/txr.1 b/txr.1
index e2f631a4..c57548a7 100644
--- a/txr.1
+++ b/txr.1
@@ -18388,8 +18388,9 @@ has no supertype.
 
 The
 .meta type
-must be either a struct type object, or else
-a symbol which names a struct type.
+argument must be either a struct type object, a
+a symbol which names a struct type (which is resolved to that type),
+or else a structure instance (which is resolved to its structure type).
 
 .coNP Function @ make-struct
 .synb