Add generic JSON-like default __repr__ to user types

trans/transpiler/phases/emit_cpp/class_.py

@@ -24,6 +24,21 @@ class ClassVisitor(NodeVisitor):
         yield "type() {}"
         yield "type(const type&) = delete;"
         yield "type(type&&) = delete;"
+
+        yield "void py_repr(std::ostream &s) const {"
+        yield "s << '{';"
+        for i, (name, memb) in enumerate(node.type.members.items()):
+            if i != 0:
+                yield 's << ", ";'
+            yield f's << "\\"{name}\\": ";'
+            yield f"repr_to({name}, s);"
+        yield "s << '}';"
+        yield "}"
+
+        yield "void py_print(std::ostream &s) const {"
+        yield "py_repr(s);"
+        yield "}"
+
         yield "};"
 
         yield "template<typename... T> auto operator()(T&&... args) {"