Main.java

// Encodes a Turing machine that counts in binary, and then halts.
// Gives stack overflow by default.
// If you increase the stack size (javac -J-Xss100M Main.java),
// then it type-checks, but it takes a lot of time.

interface Z {}
interface N<x> {}
interface ML<x> {}
interface MR<x> {}

interface L0<x> {}
interface L1<x> {}
interface LT<x> {}
interface Lhash<x> {}

interface QiwL<x> extends
  ML<N<?super QiL<?super x>>>,
  MR<N<?super QiwL<?super MR<?super N<?super x>>>>>,
  E<QiLR<?super N<?super x>>>,
  L0<N<?super QiwL<?super L0<?super N<?super x>>>>>,
  L1<N<?super QiwL<?super L1<?super N<?super x>>>>>,
  LT<N<?super QiwL<?super LT<?super N<?super x>>>>>,
  Lhash<N<?super QiwL<?super Lhash<?super N<?super x>>>>> {}
interface QfwL<x> extends
  ML<N<?super QfL<?super x>>>,
  MR<N<?super QfwL<?super MR<?super N<?super x>>>>>,
  E<QfLR<?super N<?super x>>>,
  L0<N<?super QfwL<?super L0<?super N<?super x>>>>>,
  L1<N<?super QfwL<?super L1<?super N<?super x>>>>>,
  LT<N<?super QfwL<?super LT<?super N<?super x>>>>>,
  Lhash<N<?super QfwL<?super Lhash<?super N<?super x>>>>> {}
interface QrwL<x> extends
  ML<N<?super QrL<?super x>>>,
  MR<N<?super QrwL<?super MR<?super N<?super x>>>>>,
  E<QrLR<?super N<?super x>>>,
  L0<N<?super QrwL<?super L0<?super N<?super x>>>>>,
  L1<N<?super QrwL<?super L1<?super N<?super x>>>>>,
  LT<N<?super QrwL<?super LT<?super N<?super x>>>>>,
  Lhash<N<?super QrwL<?super Lhash<?super N<?super x>>>>> {}
interface QhwL<x> extends
  ML<N<?super QhL<?super x>>>,
  MR<N<?super QhwL<?super MR<?super N<?super x>>>>>,
  E<E<?super Z>>,
  L0<N<?super QhwL<?super L0<?super N<?super x>>>>>,
  L1<N<?super QhwL<?super L1<?super N<?super x>>>>>,
  LT<N<?super QhwL<?super LT<?super N<?super x>>>>>,
  Lhash<N<?super QhwL<?super Lhash<?super N<?super x>>>>> {}

interface QiwR<x> extends
  MR<N<?super QiR<?super x>>>,
  ML<N<?super QiwR<?super ML<?super N<?super x>>>>>,
  E<QiRL<?super N<?super x>>>,
  L0<N<?super QiwR<?super L0<?super N<?super x>>>>>,
  L1<N<?super QiwR<?super L1<?super N<?super x>>>>>,
  LT<N<?super QiwR<?super LT<?super N<?super x>>>>>,
  Lhash<N<?super QiwR<?super Lhash<?super N<?super x>>>>> {}
interface QfwR<x> extends
  MR<N<?super QfR<?super x>>>,
  ML<N<?super QfwR<?super ML<?super N<?super x>>>>>,
  E<QfRL<?super N<?super x>>>,
  L0<N<?super QfwR<?super L0<?super N<?super x>>>>>,
  L1<N<?super QfwR<?super L1<?super N<?super x>>>>>,
  LT<N<?super QfwR<?super LT<?super N<?super x>>>>>,
  Lhash<N<?super QfwR<?super Lhash<?super N<?super x>>>>> {}
interface QrwR<x> extends
  MR<N<?super QrR<?super x>>>,
  ML<N<?super QrwR<?super ML<?super N<?super x>>>>>,
  E<QrRL<?super N<?super x>>>,
  L0<N<?super QrwR<?super L0<?super N<?super x>>>>>,
  L1<N<?super QrwR<?super L1<?super N<?super x>>>>>,
  LT<N<?super QrwR<?super LT<?super N<?super x>>>>>,
  Lhash<N<?super QrwR<?super Lhash<?super N<?super x>>>>> {}
interface QhwR<x> extends
  MR<N<?super QhR<?super x>>>,
  ML<N<?super QhwR<?super ML<?super N<?super x>>>>>,
  E<E<?super Z>>,
  L0<N<?super QhwR<?super L0<?super N<?super x>>>>>,
  L1<N<?super QhwR<?super L1<?super N<?super x>>>>>,
  LT<N<?super QhwR<?super LT<?super N<?super x>>>>>,
  Lhash<N<?super QhwR<?super Lhash<?super N<?super x>>>>> {}

interface E<x> extends
  QiLR<N<?super QiwR<?super E<?super E<?super x>>>>>,
  QfLR<N<?super QfwR<?super E<?super E<?super x>>>>>,
  QrLR<N<?super QrwR<?super E<?super E<?super x>>>>>,
  QhLR<N<?super QhwR<?super E<?super E<?super x>>>>>,

  QiRL<N<?super QiwL<?super E<?super E<?super x>>>>>,
  QfRL<N<?super QfwL<?super E<?super E<?super x>>>>>,
  QrRL<N<?super QrwL<?super E<?super E<?super x>>>>>,
  QhRL<N<?super QhwL<?super E<?super E<?super x>>>>> {}

interface QiLR<x> {}
interface QfLR<x> {}
interface QrLR<x> {}
interface QhLR<x> {}

interface QiRL<x> {}
interface QfRL<x> {}
interface QrRL<x> {}
interface QhRL<x> {}

interface QiL<x> extends
  LT<N<?super QfwL<?super LT<?super N<?super MR<?super N<?super x>>>>>>> {}
interface QfL<x> extends
  L0<N<?super QrwL<?super ML<?super N<?super L1<?super N<?super x>>>>>>>,
  L1<N<?super QfwL<?super L0<?super N<?super MR<?super N<?super x>>>>>>>,
  LT<N<?super QhwL<?super MR<?super N<?super LT<?super N<?super x>>>>>>> {}
interface QrL<x> extends
  L0<N<?super QrwL<?super ML<?super N<?super L0<?super N<?super x>>>>>>>,
  L1<N<?super QrwL<?super ML<?super N<?super L1<?super N<?super x>>>>>>>,
  LT<N<?super QfwL<?super LT<?super N<?super MR<?super N<?super x>>>>>>> {}
interface QhL<x> extends
  LT<N<?super QhwL<?super MR<?super N<?super LT<?super N<?super x>>>>>>> {}

interface QiR<x> extends
  LT<N<?super QfwR<?super MR<?super N<?super LT<?super N<?super x>>>>>>> {}
interface QfR<x> extends
  L0<N<?super QrwR<?super L1<?super N<?super ML<?super N<?super x>>>>>>>,
  L1<N<?super QfwR<?super MR<?super N<?super L0<?super N<?super x>>>>>>>,
  LT<N<?super QhwR<?super ML<?super N<?super LT<?super N<?super x>>>>>>> {}
interface QrR<x> extends
  L0<N<?super QrwR<?super L0<?super N<?super ML<?super N<?super x>>>>>>>,
  L1<N<?super QrwR<?super L1<?super N<?super ML<?super N<?super x>>>>>>>,
  LT<N<?super QfwR<?super MR<?super N<?super LT<?super N<?super x>>>>>>> {}
interface QhR<x> extends
  LT<N<?super QhwR<?super ML<?super N<?super LT<?super N<?super x>>>>>>> {}



class Main {
    Lhash<?super N<?super
    MR<?super N<?super
    LT<?super N<?super
    L0<?super N<?super
    L0<?super N<?super
    L0<?super N<?super
    L0<?super N<?super
    L0<?super N<?super
    L0<?super N<?super
    L0<?super N<?super
    L0<?super N<?super
    L0<?super N<?super
    L0<?super N<?super
    L0<?super N<?super
    LT<?super N<?super
    Lhash<?super N<?super
    E<?super E<?super Z>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
  doit(
    QiwR<?super E<?super E<?super Z>>> v
  ) {
    return v;
  }
}

I'd rather use Brainfuck.