check that an enum case head has the right type

haha oops

lib/Quox/Typing/Error.idr

@@ -20,6 +20,7 @@ data Error q
 | ExpectedNat  (TyContext q d n) (Term q d n)
 | BadUniverse  Universe Universe
 | TagNotIn     TagVal (SortedSet TagVal)
+| BadCaseEnum  (SortedSet TagVal) (SortedSet TagVal)
 | BadCaseQtys  (TyContext q d n) (List (QOutput q n, Term q d n, Term q d n))
 
 -- first term arg of ClashT is the type
@@ -218,6 +219,10 @@ parameters {auto _ : (Eq q, IsQty q, PrettyHL q)} (unicode : Bool)
       sep [sep ["tag", prettyTag tag, "is not contained in"],
            termt empty (Enum set)]
 
+    BadCaseEnum type arms =>
+      sep ["case expression has head of type", termt empty (Enum type),
+           "but cases for", termt empty (Enum arms)]
+
     BadCaseQtys ctx arms =>
       hang 4 $ sep $
         "inconsistent variable usage in case arms" ::