lintAlt :: Type -> (AltCon, [Id], [Bool], StgExpr) -> LintM (Maybe Type)
lintAlt _ (DEFAULT, _, _, rhs)
 = lintStgExpr rhs
lintAlt :: Type -> (AltCon, [Id], [Bool], StgExpr) -> LintM (Maybe Type)
lintAlt _ (DEFAULT, _, _, rhs)
 = lintStgExpr rhs
lintAlt _ (DEFAULT, _, _, rhs)
 = lintStgExpr rhs