Function walk

walk(
    program: Program,
    callback: (
        instruction: Instruction,
        index: number,
        program: Program,
    ) => void,
): void
Visits every instruction in order.
Parameters
- program: Program
  Program to walk.
- callback: (instruction: Instruction, index: number, program: Program) => void
  Called with each instruction, its index and the program.
Returns void