source: addons/HeuristicLab.PushGP/HeuristicLab.Problems.ProgramSynthesis/Push/Expressions/NameExpressions.cs

namespace HeuristicLab.Problems.ProgramSynthesis.Push.Expressions {
  using System.Linq;

  using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
  using HeuristicLab.Problems.ProgramSynthesis.Push.Attributes;
  using HeuristicLab.Problems.ProgramSynthesis.Push.Stack;
  using Interpreter;

  [StorableClass]
  public class NameDefineXExecExpression : StatefulExpression<string> {
    public NameDefineXExecExpression(string state) : base(state) { }
    [StorableConstructor]
    protected NameDefineXExecExpression(bool deserializing) : base(deserializing) { }

    public override bool IsNoop(IInternalPushInterpreter interpreter) {
      return false;
    }

    public override void Eval(IInternalPushInterpreter interpreter) {
      Expression expression;
      if (!interpreter.IsNameQuoteFlagSet &&
          interpreter.CustomExpressions.TryGetValue(State, out expression)) {
        interpreter.ExecStack.Push(expression);
      } else {
        interpreter.NameStack.Push(State);
        interpreter.IsNameQuoteFlagSet = false;
      }
    }
  }

  /// <summary>
  /// Sets a flag indicating that the next State encountered will be pushed onto the NAME stack (and not have its
  /// associated value pushed onto the EXEC stack), regardless of whether or not it has a definition. Upon encountering such a State and
  /// pushing it onto the NAME stack the flag will be cleared (whether or not the pushed State had a definition).
  /// </summary>
  [PushExpression(
    StackTypes.Name,
    "NAME.QUOTE",
    "Sets a flag indicating that the next State encountered will be pushed onto the NAME stack")]
  [StorableClass]
  public class NameQuoteExpression : StatelessExpression {
    public NameQuoteExpression() { }
    [StorableConstructor]
    protected NameQuoteExpression(bool deserializing) : base(deserializing) { }

    public override bool IsNoop(IInternalPushInterpreter interpreter) {
      return interpreter.IsNameQuoteFlagSet;
    }

    public override void Eval(IInternalPushInterpreter interpreter) {
      interpreter.IsNameQuoteFlagSet = true;
    }
  }

  /// <summary>
  /// Pushes a randomly selected NAME that already has a definition.
  /// </summary>
  [PushExpression(
    StackTypes.Name,
    "NAME.RANDBOUNDNAME",
    "Pushes a randomly selected NAME that already has a definition.")]
  [StorableClass]
  public class NameRandBoundNameExpression : StatelessExpression {
    public NameRandBoundNameExpression() { }
    [StorableConstructor]
    protected NameRandBoundNameExpression(bool deserializing) : base(deserializing) { }

    public override bool IsNoop(IInternalPushInterpreter interpreter) {
      return interpreter.CustomExpressions.Count == 0;
    }

    public override void Eval(IInternalPushInterpreter interpreter) {
      var index = interpreter.CustomExpressions.Keys.Count == 1
        ? 0
        : interpreter.Random.Next(0, interpreter.CustomExpressions.Keys.Count);

      var state = interpreter.CustomExpressions.Keys.ElementAt(index);
      interpreter.NameStack.Push(state);
    }
  }
}