Bug is avoided by not upcasting to same type. Bug still exists.

TODO.md

@@ -6,6 +6,9 @@ TODO
 call equal_tagged_value() when you find a union type when
 comparing structs deeply.  (C backend, probably others)
 
+There appears to be a bug with casting a union type to
+itself?  The tag in the tagged value is the union?
+
 Name mangling for compilers (prepend with `_` most likely.)
 
 And literal characters in strings, especially `'` and `"`.

eg/assoc.castile

@@ -22,7 +22,7 @@ fun lookup(a: assoc, k: string) {
     return null as string|void
   }
   typecase n is assoc {
-    return lookup(n, k) as string|void
+    return lookup(n, k)
   }
 }
 

tests/Castile.md

@@ -827,6 +827,27 @@ Deeply nested structs can be tested for equality.
     | }
     = True
 
+Deeply nested structs can be tested for equality, even when containing values
+of union type.
+
+    | struct name { first: string; last: string|integer }
+    | struct person { age: integer; name: name }
+    | main = fun() {
+    |   j = make person(age: 23, name:make name(first:"Bamber", last:"Smith" as string|integer));
+    |   k = make person(age: 23, name:make name(first:"Bamber", last:"Smith" as string|integer));
+    |   j == k
+    | }
+    = True
+
+    | struct name { first: string; last: string|integer }
+    | struct person { age: integer; name: name }
+    | main = fun() {
+    |   j = make person(age: 23, name:make name(first:"Bamber", last:"Smith" as string|integer));
+    |   k = make person(age: 23, name:make name(first:"Bamber", last:75 as string|integer));
+    |   j != k
+    | }
+    = True
+
 Structs cannot be compared for ordering.
 
     | struct person { age: integer; name: string }
@@ -1354,7 +1375,7 @@ One can use this facility to implement abstract data types.
     |     return null as string|void
     |   }
     |   typecase n is assoc {
-    |     return lookup(n, k) as string|void
+    |     return lookup(n, k)
     |   }
     | }
     |