json: support printing structs in JSON format.

* lib.c (out_json_sym): New static function.
(out_json_rec): Handle structp.

* txr.1: Documented.

2 files changed, 78 insertions, 0 deletions

diff --git a/lib.c b/lib.c
index c00e6401..03f28956 100644
--- a/lib.c
+++ b/lib.c
@@ -14820,6 +14820,16 @@ static int check_emit_circle(val obj, val out, struct strm_ctx *ctx, val self)
   return 0;
 }
 
+static void out_json_sym(val sym, val out, struct strm_ctx *ctx)
+{
+  put_char(chr('"'), out);
+  if (ctx)
+    obj_print_impl(sym, out, nil, ctx);
+  else
+    obj_print(sym, out, nil);
+  put_char(chr('"'), out);
+}
+
 static void out_json_rec(val obj, val out, enum json_fmt jf,
                          struct strm_ctx *ctx)
 {
@@ -15026,6 +15036,58 @@ static void out_json_rec(val obj, val out, enum json_fmt jf,
         force_break(out);
       return;
     }
+    if (structp(obj)) {
+      val ty = typeof(obj);
+      val sl = slots(ty);
+      val iter;
+      val save_indent;
+      int force_br = 0;
+
+      if (jf == json_fmt_standard) {
+        put_string(lit("{\n"), out);
+        save_indent = inc_indent_abs(out, two);
+        put_string(lit("\"__type\" : "), out);
+        out_json_sym(ty, out, ctx);
+
+        for (iter = sl; iter; iter = cdr(iter)) {
+          val slsym = car(iter);
+
+          if (static_slot_p(ty, slsym))
+            continue;
+
+          put_string(lit(",\n"), out);
+          out_json_sym(slsym, out, ctx);
+          put_string(lit(" : "), out);
+          out_json_rec(slot(obj, slsym), out, jf, ctx);
+        }
+        put_string(lit("\n"), out);
+      } else {
+        put_char(chr('{'), out);
+        save_indent = inc_indent(out, zero);
+        put_string(lit("\"__type\":"), out);
+        out_json_sym(ty, out, ctx);
+
+        for (iter = sl; iter; iter = cdr(iter)) {
+          val slsym = car(iter);
+
+          if (static_slot_p(ty, slsym))
+            continue;
+
+          put_string(lit(","), out);
+          if (width_check(out, nil))
+            force_br = 1;
+          out_json_sym(slsym, out, ctx);
+          put_string(lit(":"), out);
+          out_json_rec(slot(obj, slsym), out, jf, ctx);
+        }
+      }
+
+      set_indent(out, save_indent);
+      put_char(chr('}'), out);
+      if (force_br)
+        force_break(out);
+      return;
+    }
     break;
   case FLNUM:
   case NUM:
diff --git a/txr.1 b/txr.1
index 53d3377b..bda03dcc 100644
--- a/txr.1
+++ b/txr.1
@@ -84092,6 +84092,22 @@ A list of object is rendered in the same way as vector, in the JSON
 .code []
 notation. When such JSON notation is parsed, a vector is produced.
 
+A structure object is rendered into JSON using the
+.code {}
+object notation. The keys of the objects are the names of the
+symbols of the object type's non-static slots, appearing as a
+string. The values are the values of the slots. They must be JSON-conforming
+objects.
+The first entry of the object is a key named
+.str __type
+whose value is the structure type symbol, appearing as a string.
+Both the slot symbols and the type symbol may appear with a package
+qualifier, depending on the relationship of the symbols to the current
+package, according to similar rules as if the symbol were printed
+by the
+.code print
+function.
+
 When integer objects are output, they may not constitute valid JSON, since the
 JSON specification supports only IEEE 64 bit floating-point numbers. JSON
 numbers are read as floating-point.