run-gadts-strict.scala:12: error: type mismatch;
 found   : n.type (with underlying type Int)
 required: T
    case Lit(n)        => n
                          ^
run-gadts-strict.scala:13: error: type mismatch;
 found   : Int
 required: T
    case Succ(u)       => eval(u) + 1
                                  ^
run-gadts-strict.scala:14: error: type mismatch;
 found   : Boolean
 required: T
    case IsZero(u)     => eval(u) == 0
                                  ^
run-gadts-strict.scala:15: error: type mismatch;
 found   : T(in class If)
 required: T(in method eval)
    case If(c, u1, u2) => eval(if (eval(c)) u1 else u2)
                              ^
four errors found