diff --git a/redo/types.c b/redo/types.c
new file mode 100644
index 00000000..4a058160
--- /dev/null
+++ b/redo/types.c
@@ -0,0 +1,53 @@
+// 17 may 2015
+#include "out/ui.h"
+#include "uipriv.h"
+
+struct typeinfo {
+	const char *name;
+	uintmax_t parent;
+};
+
+static struct ptrArray *types = NULL;
+
+uintmax_t uiRegisterType(const char *name, uintmax_t parent)
+{
+	struct typeinfo *ti;
+
+	if (types == NULL) {
+		types = newPtrArray();
+		// reserve ID 0
+		ptrArrayAppend(types, NULL);
+	}
+	ti = uiNew(struct typeinfo);
+	ti->name = name;
+	ti->parent = parent;
+	ptrArrayAppend(types, ti);
+	return types->len - 1;
+}
+
+void *uiIsA(void *p, uintmax_t id)
+{
+	uiTyped *t;
+	struct typeinfo *ti;
+	uintmax_t compareTo;
+
+	if (id == 0 || id >= types->len)
+		complain("invalid type ID given to uiIsA()");
+	t = (uiTyped *) p;
+	compareTo = t->Type;
+	for (;;) {
+		if (compareTo == 0 || compareTo >= types->len)
+			complain("invalid type ID in uiIsA()", t);
+		if (compareTo == id)
+			return t;
+		ti = ptrArrayIndex(types, struct typeinfo *, t->Type);
+		if (ti->parent == 0)
+			break;
+		compareTo = ti->parent;
+	}
+	ti = ptrArrayIndex(types, struct typeInfo *, t->Type);
+	complain("object %p not a %s in uiIsA()", t, ti->name);
+	return NULL;			// make compiler happy
+}
+
+// TODO free type info
diff --git a/redo/ui.idl b/redo/ui.idl
index 0d4f2afa..e27cb0ec 100644
--- a/redo/ui.idl
+++ b/redo/ui.idl
@@ -28,6 +28,12 @@ func OnShouldQuit(f *func(data *void) int, data *void);
 
 func FreeText(text *char);
 
+func RegisterType(name *const char, parent uintmax_t);
+func IsA(p *void, type uintmax_t);
+struct uiTyped {
+	field Type uintmax_t;
+};
+
 raw "typedef struct uiSizingSys uiSizingSys;";
 
 struct Sizing {