sm.cs

public IEnumerable<Instruction> Transpiler(IEnumerable<Instruction> codes) 
{
  var state = TranspilerState.Initial;
  foreach (var code of codes)
  {
    switch (state)
    {
      case TranspilerState.Initial:
        if (SomeCondition(code))
        {
          state = TranspilerState.HitPattern;
        }
        break;
      case TranspilerState.HitPattern:
        return yield whatever;
        return yield whatever;
        return yield code;
        state = TranspilerState.Done;
        break;
      case TranspilerState.Done:
        yield return code;
        break; 
      default
        throw new Exception("Invalid state");
    }
  }
}