Click here to Skip to main content
Click here to Skip to main content
Add your own
alternative version

Implementing Programming Languages Using C# 4.0

, 12 Jul 2012 MIT
An introduction to creating programming language tools using C# 4.0.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Rudiments.Miscellaney
{
    public class TheoremProver
    {
        public class Term
        {
            public List<Term> Arguments = new List<Term>(); 
            public int Arity { get { return Arguments.Count; } }
        }

        public class Atom : Term
        {
            public string Name;
            public bool Equivalent(Atom a) { return Name == a.Name; }
        }

        public class Variable : Atom
        {
        }        

        public class Constant : Atom
        {
        }

        public class Compound : Term
        {
            public Atom Functor;
        }

        public class Relation 
        {
            public Term Head;
            public Term Body;
        }

        public class Database
        {
            List<Term> Facts;
            List<Relation> Relations;
        }

        public class Bindings
        {
            Dictionary<string, Term> dictionary = new Dictionary<string,Term>();

            public Bindings()
            {
            }

            public Bindings(Bindings other)
            {
                foreach (var kv in other.dictionary)
                    dictionary.Add(kv.Key, kv.Value);
            }

            public void Add(Variable v, Term t)
            {
                if (dictionary.ContainsKey(v.Name))
                    throw new Exception(String.Format("{0} is already bound", v.Name));
                dictionary.Add(v.Name, t);
            }

            public Bindings Clone()
            {
                return new Bindings(this);
            }
        }

        public class Unifier
        {
            public class UnificationFailure : Exception { }
            public class CyclicalBinding : Exception { }

            public IEnumerable<Bindings> Unify(Term t1, Term t2, Bindings bindings) 
            {
                if (t1.Arity != t2.Arity)
                    throw new UnificationFailure();

                Bindings result = bindings.Clone();
                
                if (t1 is Variable)
                {
                    result.Add((Variable)t1, t2);
                    yield return result;
                }
                else if (t2 is Variable)
                {                    
                    bindings.Add((Variable)t2, t1);
                    yield return result;
                }
                else if (t1 is Constant && t2 is Constant)
                {
                    if (!((Constant)t1).Equals((Constant)t2))
                        throw new UnificationFailure();
                    yield return result;
                }
                else
                {
                    if (t1.Arity == 0)
                        yield return result;

                    // I think I need to make a list ofa all of the bindings that were added. 
                    // If a failure occurs, then this unification fails. 
                    // The other question is where does the variable matching come into play. 
                    for (int i = 0; i < t1.Arity; ++i)
                            foreach (var b in Unify(t1.Arguments[i], t2.Arguments[i], bindings))
                                yield return b;
                }
            }
        }
    }
}

By viewing downloads associated with this article you agree to the Terms of Service and the article's licence.

If a file you wish to view isn't highlighted, and is a text file (not binary), please let us know and we'll add colourisation support for it.

License

This article, along with any associated source code and files, is licensed under The MIT License

Share

About the Author

Christopher Diggins
Software Developer Autodesk
Canada Canada
This article was written by Christopher Diggins, a computer science nerd who currently works at Autodesk as an SDK specialist.
Follow on   Twitter   Google+   LinkedIn

| Advertise | Privacy | Terms of Use | Mobile
Web01 | 2.8.150224.1 | Last Updated 12 Jul 2012
Article Copyright 2011 by Christopher Diggins
Everything else Copyright © CodeProject, 1999-2015
Layout: fixed | fluid