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Description: compile-time insanity
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typedef bool red; typedef bool blue; typedef bool green; typedef bool white;

struct cube(U, F, R, B, L, D) {
  alias U Up; alias F Front;
  alias R Right; alias B Back;
  alias L Left; alias D Down;
}

template tuple(T...) { alias T tuple; }

alias cube!(blue, green, white, green, blue, red) cube1;
alias cube!(white, green, blue, white, red, red) cube2;
alias cube!(green, white, red, blue, red, red) cube3;
alias cube!(blue, red, green, green, white, white) cube4;

alias tuple!(cube1, cube2, cube3, cube4) cubes;

template Rotation(C) {
  alias cube!(C.Up, C.Right, C.Back, C.Left, C.Front, C.Down) Rotation;
}

template Twist(C) {
  alias cube!(C.Front, C.Right, C.Up, C.Left, C.Down, C.Back) Twist;
}

template Flip(C) {
  alias cube!(C.Down, C.Left, C.Back, C.Right, C.Front, C.Up) Flip;
}

template Rotations(C) {
  alias tuple!(C, Rotation!(C),
    Rotation!(Rotation!(C)), Rotation!(Rotation!(Rotation!(C)))
  ) Rotations;
}

template Twists(C) {
  alias tuple!(C, Twist!(C), Twist!(Twist!(C))) Twists;
}

template Flips(C) {
  alias tuple!(C, Flip!(C)) Flips;
}

template map(alias T, U...) {
  static if (U.length) alias tuple!(T!(U[0]), map!(T, U[1..$])) map;
  else alias tuple!() map;
}

template _Orientations(C) {
  alias Rotations!(C) rots;
  alias map!(Twists, rots) twists;
  alias map!(Flips, twists) orients;
}

template Orientations(C) { alias _Orientations!(C).orients Orientations; }

template Compatible(C1, C2) {
  const bool Compatible=!is(C1.Front==C2.Front)
        &&!is(C1.Back==C2.Back)
        &&!is(C1.Right==C2.Right)
        &&!is(C1.Left==C2.Left);
}

template Allowed(C, Pile...) {
  static if (!Pile.length) const bool Allowed=true;
  else const bool Allowed=Compatible!(C, Pile[$-1]) && Allowed!(C, Pile[0..$-1]);
}

// At this point I have ceased to understand the C++ program.
// The rest is made-up.
//        :-)

void iteratePiles(T...)() {
  static if (T.length==4) pragma(msg, "Valid solution: "~T.stringof);
  else {
    foreach (newface; Orientations!(cubes[T.length]))
      static if (Allowed!(newface, T)) iteratePiles!(T, newface)();
  }
}

void main() { iteratePiles!()(); }

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