Think Design Pattern in psuedo-code

Design pattern are abstract and hard to explain in words. But code seems simple

Visitor -- IAccept IVisitor

public interface IVisitor { Visit(Stock s);Visit(Option o);}
public interface IAccpet { void Accept(IVisitor v);}

public class Option : IAccpet {
    public void Accept(IVisitor v) { v.Visit(this);}
}
public class Stock : IAccpet {
    public void Accept(IVisitor v) {v.Visit(this); }
}

public class PnLVisitor : IVisitor {
  void Visit(Option o) { } void Visit(Stock s) { } }

public class Trader
{
    List<IAccpet> _holdings = new List<IAccpet>() { new Stock(), new Option() };
    void CalcPnl() { foreach (var h in _holdings) h.Accept(new PnLVisitor()); }
}

Decorator---avoid sub-classing by composition/Wrapper
// eg. BufferStream(NetwokStream) since NS no buf
abstract class BaseComponent { }

class Decorator
{
    protected BaseComponent _base;
    // need to pass in concrete one

    public Decorator(BaseComponent b){_base = b;}
}

Strategy --extend not modify
// new Strat extend for the same ctx
// avoid switch statement, call svc varying strat
public interface IStrategy { double Calculate();}

public class OptoinStrategy : IStrategy {
    public OptoinStrategy(Context ctx) {}

    public double Calculate(){return strategyValue;}
}

public class Context { }
public class Service {
    IStrategy _strat;
    public Service(IStrategy strat){ _strat = strat;} 
    public double Calc(){return _strat.Calculate();}
}