Instance.cs

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using Mercury.Nucleus.Trees;
using Mercury.Syntax;
using System;
using System.Collections.Generic;
using System.Linq;

namespace Mercury.Interpreting
{
//=============================================================================
//  Instance
//=============================================================================

    public class Instance : IEquatable<Instance>
    {
        //--[  Private constructors  ]-----------------------------------------

        private Instance(Variable var, object value)
        {
            if (var   == null) throw new ArgumentNullException("var");
            if (value == null) throw new ArgumentNullException("value");

            Var   = var;
            Value = value;
        }

        //--[  Constructors  ]-------------------------------------------------

        // used by Wildcard
        internal Instance(Variable var, Tree<Symbol>[] wildmatch)
            : this(var, wildmatch as object)
        { }

        internal Instance(Variable var, Tree<Symbol> tree)
            : this(var, tree as object)
        { }

        //--[  Properties  ]---------------------------------------------------

        public Variable Var   { get; private set; }

        public object Value { get; private set; }

        //--[  Overriden methods  ]--------------------------------------------

        #region [  Object      ]

        public override bool Equals(object obj)
        {
            Instance other = obj as Instance;
            return other == null ? false : Equals(other);
        }

        public override int GetHashCode()
        { return Var.GetHashCode(); }

        #endregion

        //--[  Interface implementation  ]-------------------------------------

        #region [  IEquatable  ]

        public bool Equals(Instance other)
        {
            if ((other == null) || !Var.Equals(other.Var))
                return false;
                
            if (Var is Wildcard)
            {
                var obja =       Value as Tree<Symbol>[];
                var objb = other.Value as Tree<Symbol>[];

                return (obja.Length == objb.Length)
                    && (obja.Zip(objb, (a, b) => a.Equals(b)).All(x => x));
            }

            return Value.Equals(other.Value);
        }

        #endregion

    }

//=============================================================================
//  InstanceList
//=============================================================================

    public class InstanceList : IEnumerable<Instance>
    {
        //--[  Private fields  ]-----------------------------------------------

        private List<Instance>               data;
        private Dictionary<string, Instance> dict;

        //--[  Constructors  ]-------------------------------------------------

        internal InstanceList()
        {
            data = new List<Instance>();
            dict = new Dictionary<string, Instance>();
        }

        //--[  Properties  ]---------------------------------------------------

        public int Count { get { return data.Count; } }

        //--[  Indexer  ]------------------------------------------------------

        public Instance this[string name] { get { return dict[name]; } }

        //--[  Methods  ]------------------------------------------------------

        internal void Add(Instance instance)
        {
            if (instance == null) throw new ArgumentNullException("instance");
            
            dict.Add(instance.Var.Name, instance);
            data.Add(instance);
        }

        internal void Clear()
        {
            dict.Clear();
            data.Clear();
        }

        internal void RemoveLast(int count = 1)
        {
            for(int ix = 0; (ix < count) && (data.Count > 0); ++ix)
            {
                Instance value = data[data.Count - 1];
                data.RemoveAt(data.Count - 1);
                dict.Remove(value.Var.Name);
            }
        }

        //--[  Interface implementation  ]-------------------------------------

        #region [  IEnumerable  ]

        public IEnumerator<Instance> GetEnumerator()
        { return data.GetEnumerator(); }

        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
        { return data.GetEnumerator(); }

        #endregion

    }

}