lintAlt scrut_ty (LitAlt lit, _, _, rhs) = do
   checkTys (literalType lit) scrut_ty (mkAltMsg1 scrut_ty)
   lintStgExpr rhs
lintAlt scrut_ty (LitAlt lit, _, _, rhs) = do
   checkTys (literalType lit) scrut_ty (mkAltMsg1 scrut_ty)
   lintStgExpr rhs
lintAlt scrut_ty (LitAlt lit, _, _, rhs) = do
   checkTys (literalType lit) scrut_ty (mkAltMsg1 scrut_ty)
   lintStgExpr rhs