Links enable a constrained machine to call into another machine.

machine Main(latch, operation_id) {
    Arith adder;

    operation main<0> x, y -> z;

    // - on every row (the boolean flag is `1`)
    // - constrain the values of `x`, `y`, and `z` so that `z = adder.add(x, y)`
    // TODO: uncomment the link once witness generation supports it
    // link 1 x, y -> z = adder.add;

    col fixed operation_id = [0]*;
    col fixed latch = [1]*;

    col witness x;
    col witness y;
    col witness z;

They are defined by:

  • a boolean flag which must be on for the link to be active
  • parameters to pass to the other machine, in the form of columns defined in the current machine
  • an operation or function of the machine which is called