source: branches/PushGP/HeuristicLab.PushGP/HeuristicLab.Problems.ProgramSynthesis/Push/Expressions/DoRangeExpressions.cs @ 14744

namespace HeuristicLab.Problems.ProgramSynthesis.Push.Expressions {
  using Attributes;
  using Interpreter;
  using Stack;

  public abstract class DoRangeExpression : LoopExpression {
    protected DoRangeExpression() { }
    protected DoRangeExpression(LoopState state) : base(state) { }
    protected override bool HasInsufficientArguments(IPushInterpreter interpreter, IStack<Expression> sourceStack) {
      return interpreter.IntegerStack.Count < 2 ||
             sourceStack.Count == 0 ||
             interpreter.IntegerStack.Top == interpreter.IntegerStack.ReverseElementAt(1);
    }

    protected override LoopState InitState(IPushInterpreter interpreter, IStack<Expression> sourceStack) {
      var destinationIndex = interpreter.IntegerStack.Pop();
      var incrementor = destinationIndex < interpreter.IntegerStack.Top ? -1 : 1;

      return new LoopState(
          body: sourceStack.Pop(),
          currentIndex: interpreter.IntegerStack.Top + incrementor,
          destinationIndex: destinationIndex,
          incrementor: incrementor);
    }
  }

  /// <summary>
  ///     An iteration instruction that executes the top item on the CODE stack a number of times that depends on the
  ///     top two integers, while also pushing the loop counter onto the INTEGER stack for possible access during the
  ///     execution of
  ///     the body of the loop. The top integer is the "destination index" and the second integer is the "current index."
  ///     First the code
  ///     and the integer arguments are saved locally and popped. Then the integers are compared. If the integers are equal
  ///     then the current
  ///     index is pushed onto the INTEGER stack and the code (which is the "body" of the loop) is pushed onto the EXEC stack
  ///     for subsequent
  ///     execution. If the integers are not equal then the current index will still be pushed onto the INTEGER stack but two
  ///     items will be
  ///     pushed onto the EXEC stack -- first a recursive call to CODE.DO*RANGE (with the same code and destination index,
  ///     but with a current
  ///     index that has been either incremented or decremented by 1 to be closer to the destination index) and then the body
  ///     code. Note that
  ///     the range is inclusive of both endpoints; a call with integer arguments 3 and 5 will cause its body to be executed
  ///     3 times, with the
  ///     loop counter having the values 3, 4, and 5. Note also that one can specify a loop that "counts down" by providing a
  ///     destination index
  ///     that is less than the specified current index.
  /// </summary>
  [PushExpression(StackType.Code, "CODE.DO*RANGE")]
  public class CodeDoRangeExpression : DoRangeExpression {
    public CodeDoRangeExpression() { }

    public CodeDoRangeExpression(LoopState state) : base(state) { }
    public override bool Eval(IPushInterpreter interpreter) {
      return this.Eval(interpreter, interpreter.CodeStack);
    }

    protected override LoopExpression Clone(LoopState state) {
      return new CodeDoRangeExpression(state);
    }
  }

  /// <summary>
  ///     An iteration instruction that executes the top item on the EXEC stack a number of times that depends on the top two
  ///     integers,
  ///     while also pushing the loop counter onto the INTEGER stack for possible access during the execution of the body of
  ///     the loop.
  ///     This is similar to CODE.DO*COUNT except that it takes its code argument from the EXEC stack. The top integer is the
  ///     "destination index" and the second integer is the "current index." First the code and the integer arguments are
  ///     saved locally
  ///     and popped. Then the integers are compared. If the integers are equal then the current index is pushed onto the
  ///     INTEGER stack
  ///     and the code (which is the "body" of the loop) is pushed onto the EXEC stack for subsequent execution. If the
  ///     integers are not
  ///     equal then the current index will still be pushed onto the INTEGER stack but two items will be pushed onto the EXEC
  ///     stack
  ///     -- first a recursive call to EXEC.DO*RANGE (with the same code and destination index, but with a current index that
  ///     has been
  ///     either incremented or decremented by 1 to be closer to the destination index) and then the body code. Note that the
  ///     range is
  ///     inclusive of both endpoints; a call with integer arguments 3 and 5 will cause its body to be executed 3 times, with
  ///     the loop
  ///     counter having the values 3, 4, and 5. Note also that one can specify a loop that "counts down" by providing a
  ///     destination
  ///     index that is less than the specified current index.
  /// </summary>
  [PushExpression(StackType.Exec, "EXEC.DO*RANGE")]
  public class ExecDoRangeExpression : DoRangeExpression {
    public ExecDoRangeExpression() { }

    public ExecDoRangeExpression(LoopState state) : base(state) { }
    public override bool Eval(IPushInterpreter interpreter) {
      return this.Eval(interpreter, interpreter.ExecStack);
    }
    protected override LoopExpression Clone(LoopState state) {
      return new ExecDoRangeExpression(state);
    }
  }
}