Print method on objects.

* struct.c (print_s): New symbol variable.
(struct_init): Initialize print_s.
(struct_inst_print): If pretty-printing, try to look
up object's print method and use it.

* txr.1: Documented pretty-printing via print method.

1 files changed, 10 insertions, 1 deletions

diff --git a/struct.c b/struct.c
index 2318ee8b..21a3a18a 100644
--- a/struct.c
+++ b/struct.c
@@ -76,7 +76,7 @@ struct struct_inst {
   val slot[1];
 };
 
-val struct_type_s, meth_s;
+val struct_type_s, meth_s, print_s;
 
 static cnum struct_id_counter;
 static val struct_type_hash;
@@ -98,6 +98,7 @@ void struct_init(void)
           convert(val *, 0));
   struct_type_s = intern(lit("struct-type"), user_package);
   meth_s = intern(lit("meth"), user_package);
+  print_s = intern(lit("print"), user_package);
   struct_type_hash = make_hash(nil, nil, nil);
   slot_hash = make_hash(nil, nil, t);
   struct_type_finalize_f = func_n1(struct_type_finalize);
@@ -985,6 +986,14 @@ static void struct_inst_print(val obj, val out, val pretty)
                                        num_fast(indent_data));
   val save_indent, iter, once;
 
+  if (pretty) {
+    loc ptr = lookup_static_slot_load(st->self, st, print_s);
+    if (!nullocp(ptr)) {
+      funcall2(deref(ptr), obj, out);
+      return;
+    }
+  }
+
   put_string(lit("#S("), out);
   obj_print_impl(st->name, out, pretty);
   save_indent = inc_indent(out, one);