/System.Xronos/Language/FunctionHelper.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using Microsoft.Runtime.CompilerServices;

using System.Xronos.Scripting.Binders;

using Microsoft.Linq.Expressions;



namespace System.Xronos.Language

{

    public static class FunctionHelper

    {

        public static T Invoke<T>(object func, ISequence args)

        {

            var newArgs = new List<object>();

            while (args != null)

            {

                newArgs.Add(args.first());

                args = args.rest();

            }

            return Invoke<T>(func, newArgs.ToArray());

        }



        static List<Func<object, object[], object>> cache = new List<Func<object, object[], object>>();

        public static T Invoke<T>(object func, params object[] args)

        {

            var c = args.Length;

            Func<object, object[], object> functor;

            if (cache.Count <= c || (functor = cache[c]) == null)

            {

                while (cache.Count <= c)

                    cache.Add(null);

                functor = cache[c] = Build(c);

            }

            return (T)functor(func, args);

        }



        private static Func<object, object[], object> Build(int argCount)

        {

            var ps = new ParameterExpression[2];

            ps[0] = Expression.Parameter(typeof(object));

            ps[1] = Expression.Parameter(typeof(object[]));



            var args = new List<Expression>();

            args.Add(ps[0]);

            for (int i = 0; i < argCount; i++)

                args.Add(Expression.ArrayIndex(ps[1], Expression.Constant(i)));



            var lambda = Expression.Lambda<Func<object, object[], object>>(

                Expression.Dynamic(BinderFactory.CachedInvoke(argCount), typeof(object), args),

                ps);



            return lambda.Compile();

        }



        public static object ThrowArity(object o)

        {

            throw new ArgumentException("Wrong number of args passed to: " + o.GetType().Name);

        }

    }

}