/// <summary>
        /// Tries to create an XPath Function expression if the function Uri correseponds to a supported XPath Function.
        /// </summary>
        /// <param name="u">Function Uri.</param>
        /// <param name="args">Function Arguments.</param>
        /// <param name="scalarArgs">Scalar Arguments.</param>
        /// <param name="expr">Generated Expression.</param>
        /// <returns>Whether an expression was successfully generated.</returns>
        public bool TryCreateExpression(Uri u, List <ISparqlExpression> args, Dictionary <String, ISparqlExpression> scalarArgs, out ISparqlExpression expr)
        {
            // If any Scalar Arguments are present then can't possibly be an XPath Function
            if (scalarArgs.Count > 0)
            {
                expr = null;
                return(false);
            }

            String func = u.AbsoluteUri;

            if (func.StartsWith(XPathFunctionsNamespace))
            {
                func = func.Substring(XPathFunctionsNamespace.Length);
                ISparqlExpression xpathFunc = null;

                switch (func)
                {
                case Absolute:
                    if (args.Count == 1)
                    {
                        xpathFunc = new AbsFunction(args.First());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath abs() function");
                    }
                    break;

                case AdjustDateTimeToTimezone:
                    throw new NotSupportedException("XPath adjust-dateTime-to-timezone() function is not supported");

                case Boolean:
                    if (args.Count == 1)
                    {
                        xpathFunc = new BooleanFunction(args.First());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath boolean() function");
                    }
                    throw new NotSupportedException("XPath boolean() function is not supported");

                case Ceiling:
                    if (args.Count == 1)
                    {
                        xpathFunc = new CeilingFunction(args.First());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath ceiling() function");
                    }
                    break;

                case Compare:
                    if (args.Count == 2)
                    {
                        xpathFunc = new CompareFunction(args.First(), args.Last());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath compare() function");
                    }
                    break;

                case Concat:
                    if (args.Count == 2)
                    {
                        xpathFunc = new ConcatFunction(args.First(), args.Last());
                    }
                    else if (args.Count > 2)
                    {
                        xpathFunc = new ConcatFunction(args);
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath concat() function");
                    }
                    break;

                case Contains:
                    if (args.Count == 2)
                    {
                        xpathFunc = new ContainsFunction(args.First(), args.Last());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath contains() function");
                    }
                    break;

                case DayFromDateTime:
                    if (args.Count == 1)
                    {
                        xpathFunc = new DayFromDateTimeFunction(args.First());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath day-from-dateTime() function");
                    }
                    break;

                case EncodeForURI:
                    if (args.Count == 1)
                    {
                        xpathFunc = new EncodeForUriFunction(args.First());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath encode-for-uri() function");
                    }
                    break;

                case EndsWith:
                    if (args.Count == 2)
                    {
                        xpathFunc = new EndsWithFunction(args.First(), args.Last());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath ends-with() function");
                    }
                    break;

                case EscapeHtmlURI:
                    if (args.Count == 1)
                    {
                        xpathFunc = new EscapeHtmlUriFunction(args.First());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath escape-html-uri() function");
                    }
                    break;

                case False:
                    if (args.Count == 0)
                    {
                        xpathFunc = new ConstantTerm(new BooleanNode(null, false));
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath false() function");
                    }
                    break;

                case Floor:
                    if (args.Count == 1)
                    {
                        xpathFunc = new FloorFunction(args.First());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath floor() function");
                    }
                    break;

                case HoursFromDateTime:
                    if (args.Count == 1)
                    {
                        xpathFunc = new HoursFromDateTimeFunction(args.First());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath hours-from-dateTime() function");
                    }
                    break;

                case LowerCase:
                    if (args.Count == 1)
                    {
                        xpathFunc = new LowerCaseFunction(args.First());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath lower-case() function");
                    }
                    break;

                case Matches:
                    if (args.Count == 2)
                    {
                        xpathFunc = new Functions.Sparql.Boolean.RegexFunction(args.First(), args.Last());
                    }
                    else if (args.Count == 3)
                    {
                        xpathFunc = new Functions.Sparql.Boolean.RegexFunction(args.First(), args[1], args.Last());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath matches() function");
                    }
                    break;

                case MinutesFromDateTime:
                    if (args.Count == 1)
                    {
                        xpathFunc = new MinutesFromDateTimeFunction(args.First());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath minutes-from-dateTime() function");
                    }
                    break;

                case MonthFromDateTime:
                    if (args.Count == 1)
                    {
                        xpathFunc = new MonthFromDateTimeFunction(args.First());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath month-from-dateTime() function");
                    }
                    break;

                case NormalizeSpace:
                    if (args.Count == 1)
                    {
                        xpathFunc = new NormalizeSpaceFunction(args.First());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath normalize-space() function");
                    }
                    break;

                case NormalizeUnicode:
                    if (args.Count == 1)
                    {
                        xpathFunc = new NormalizeUnicodeFunction(args.First());
                    }
                    else if (args.Count == 2)
                    {
                        xpathFunc = new NormalizeUnicodeFunction(args.First(), args.Last());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath normalize-space() function");
                    }
                    break;

                case Not:
                    if (args.Count == 1)
                    {
                        xpathFunc = new NotExpression(args.First());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath not() function");
                    }
                    break;

                case Replace:
                    if (args.Count == 3)
                    {
                        xpathFunc = new ReplaceFunction(args.First(), args[1], args.Last());
                    }
                    else if (args.Count == 4)
                    {
                        xpathFunc = new ReplaceFunction(args.First(), args[1], args[2], args.Last());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath replace() function");
                    }
                    break;

                case Round:
                    if (args.Count == 1)
                    {
                        xpathFunc = new RoundFunction(args.First());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath round() function");
                    }
                    break;

                case RoundHalfToEven:
                    if (args.Count == 1)
                    {
                        xpathFunc = new RoundHalfToEvenFunction(args.First());
                    }
                    else if (args.Count == 2)
                    {
                        xpathFunc = new RoundHalfToEvenFunction(args.First(), args.Last());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath round-half-to-even() function");
                    }
                    break;

                case SecondsFromDateTime:
                    if (args.Count == 1)
                    {
                        xpathFunc = new SecondsFromDateTimeFunction(args.First());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath seconds-from-dateTime() function");
                    }
                    break;

                case StartsWith:
                    if (args.Count == 2)
                    {
                        xpathFunc = new StartsWithFunction(args.First(), args.Last());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath starts-with() function");
                    }
                    break;

                case StringJoin:
                    if (args.Count == 1)
                    {
                        xpathFunc = new AggregateTerm(new StringJoinAggregate(args.First()));
                    }
                    else if (args.Count == 2)
                    {
                        xpathFunc = new AggregateTerm(new StringJoinAggregate(args.First(), args.Last()));
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath string-join() function");
                    }
                    break;

                case StringLength:
                    if (args.Count == 1)
                    {
                        xpathFunc = new StringLengthFunction(args.First());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath string-length() function");
                    }
                    break;

                case Substring:
                    if (args.Count == 2)
                    {
                        xpathFunc = new SubstringFunction(args.First(), args.Last());
                    }
                    else if (args.Count == 3)
                    {
                        xpathFunc = new SubstringFunction(args.First(), args[1], args.Last());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath substring() function");
                    }
                    break;

                case SubstringAfter:
                    if (args.Count == 2)
                    {
                        xpathFunc = new SubstringAfterFunction(args.First(), args.Last());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath substring-after() function");
                    }
                    break;

                case SubstringBefore:
                    if (args.Count == 2)
                    {
                        xpathFunc = new SubstringBeforeFunction(args.First(), args.Last());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath substring-before() function");
                    }
                    break;

                case TimezoneFromDateTime:
                    if (args.Count == 1)
                    {
                        xpathFunc = new TimezoneFromDateTimeFunction(args.First());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath timezone-from-dateTime() function");
                    }
                    break;

                case Translate:
                    throw new NotSupportedException("XPath translate() function is not supported");

                case True:
                    if (args.Count == 0)
                    {
                        xpathFunc = new ConstantTerm(new BooleanNode(null, true));
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath true() function");
                    }
                    break;

                case UpperCase:
                    if (args.Count == 1)
                    {
                        xpathFunc = new UpperCaseFunction(args.First());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath upper-case() function");
                    }
                    break;

                case YearFromDateTime:
                    if (args.Count == 1)
                    {
                        xpathFunc = new YearFromDateTimeFunction(args.First());
                    }
                    else
                    {
                        throw new RdfParseException("Incorrect number of arguments for the XPath year-from-dateTime() function");
                    }
                    break;
                }

                if (xpathFunc != null)
                {
                    expr = xpathFunc;
                    return(true);
                }
            }
            expr = null;
            return(false);
        }
        /// <summary>
        /// Tries to create a SPARQL Function expression if the function Uri correseponds to a supported SPARQL Function
        /// </summary>
        /// <param name="u">Function Uri</param>
        /// <param name="args">Function Arguments</param>
        /// <param name="scalarArguments">Scalar Arguments</param>
        /// <param name="expr">Generated Expression</param>
        /// <returns>Whether an expression was successfully generated</returns>
        public bool TryCreateExpression(Uri u, List<ISparqlExpression> args, Dictionary<string, ISparqlExpression> scalarArguments, out ISparqlExpression expr)
        {
            String func = u.ToString();
            if (func.StartsWith(SparqlFunctionsNamespace))
            {
                func = func.Substring(SparqlBuiltInFunctionFactory.SparqlFunctionsNamespace.Length);
                func = func.ToUpper();

                //If any Scalar Arguments are present then can't be a SPARQL Function UNLESS it is
                //a GROUP_CONCAT function and it has the SEPARATOR argument
                if (scalarArguments.Count > 0)
                {
                    if (func.Equals(SparqlSpecsHelper.SparqlKeywordGroupConcat) && scalarArguments.Count == 1 && scalarArguments.ContainsKey(SparqlSpecsHelper.SparqlKeywordSeparator))
                    {
                        //OK
                    }
                    else
                    {
                        expr = null;
                        return false;
                    }
                }

                //Q: Will there be special URIs for the DISTINCT modified forms of aggregates?

                ISparqlExpression sparqlFunc = null;
                switch (func)
                {
                    case SparqlSpecsHelper.SparqlKeywordAbs:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new AbsFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL ABS() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordAvg:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new AggregateTerm(new AverageAggregate(args.First()));
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL AVG() aggregate");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordBound:
                        if (args.Count == 1)
                        {
                            if (args[0] is VariableTerm)
                            {
                                sparqlFunc = new BoundFunction((VariableTerm)args[0]);
                            }
                            else
                            {
                                throw new RdfParseException("The SPARQL BOUND() function only operates over Variables");
                            }
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL BOUND() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordCeil:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new CeilFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL CEIL() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordCoalesce:
                        if (args.Count >= 1)
                        {
                            sparqlFunc = new CoalesceFunction(args);
                        }
                        else
                        {
                            throw new RdfParseException("The SPARQL COALESCE() function requires at least 1 argument");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordConcat:
                        if (args.Count >= 1)
                        {
                            sparqlFunc = new ConcatFunction(args);
                        }
                        else
                        {
                            throw new RdfParseException("The SPARQL CONCAT() function requires at least 1 argument");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordContains:
                        if (args.Count == 2)
                        {
                            sparqlFunc = new ContainsFunction(args[0], args[1]);
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL CONTAINS() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordCount:
                        //Q: What will the URIs be for the special forms of COUNT?
                        if (args.Count == 1)
                        {
                            sparqlFunc = new AggregateTerm(new CountAggregate(args.First()));
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL COUNT() aggregate");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordDataType:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new DataTypeFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL DATATYPE() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordDay:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new DayFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL DAY() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordEncodeForUri:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new EncodeForUriFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL ENCODE_FOR_URI() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordFloor:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new FloorFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL FLOOR() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordGroupConcat:
                        if (args.Count == 1)
                        {
                            if (scalarArguments.ContainsKey(SparqlSpecsHelper.SparqlKeywordSeparator))
                            {
                                sparqlFunc = new AggregateTerm(new GroupConcatAggregate(args.First(), scalarArguments[SparqlSpecsHelper.SparqlKeywordSeparator]));
                            }
                            else
                            {
                                sparqlFunc = new AggregateTerm(new GroupConcatAggregate(args.First()));
                            }
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL GROUP_CONCAT() aggregate");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordHours:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new HoursFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL HOURS() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordIf:
                        if (args.Count == 3)
                        {
                            sparqlFunc = new IfElseFunction(args[0], args[1], args[2]);
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL IF() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordIri:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new IriFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL IRI() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordIsBlank:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new IsBlankFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL ISBLANK() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordIsIri:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new IsIriFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL ISIRI() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordIsLiteral:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new IsLiteralFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL ISLITERAL() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordIsNumeric:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new IsNumericFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL ISNUMERIC() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordIsUri:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new IsUriFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL ISURI() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordLang:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new LangFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL LANG() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordLangMatches:
                        if (args.Count == 2)
                        {
                            sparqlFunc = new LangMatchesFunction(args[0], args[1]);
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL LANGMATCHES() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordLCase:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new LCaseFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL LCASE() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordMax:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new AggregateTerm(new MaxAggregate(args.First()));
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL MAX() aggregate");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordMD5:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new MD5HashFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL CONTAINS() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordMin:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new AggregateTerm(new MinAggregate(args.First()));
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL MIN() aggregate");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordMinutes:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new MinutesFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL MINUTES() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordMonth:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new MonthFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL MONTH() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordNow:
                        if (args.Count == 0)
                        {
                            sparqlFunc = new NowFunction();
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL ABS() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordRegex:
                        if (args.Count == 2)
                        {
                            sparqlFunc = new RegexFunction(args[0], args[1]);
                        }
                        else if (args.Count == 3)
                        {
                            sparqlFunc = new RegexFunction(args[0], args[1], args[2]);
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL REGEX() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordRound:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new RoundFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL ROUND() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordSameTerm:
                        if (args.Count == 2)
                        {
                            sparqlFunc = new SameTermFunction(args[0], args[1]);
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL SAMETERM() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordSample:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new AggregateTerm(new SampleAggregate(args.First()));
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL AVG() aggregate");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordSeconds:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new SecondsFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL SECONDS() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordSha1:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new Sha1HashFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL SHA1() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordSha256:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new Sha256HashFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL SHA256() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordSha384:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new Sha384HashFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL SHA384() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordSha512:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new Sha512HashFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL SHA512() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordStr:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new StrFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL STR() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordStrDt:
                        if (args.Count == 2)
                        {
                            sparqlFunc = new StrDtFunction(args[0], args[1]);
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL STRDT() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordStrEnds:
                        if (args.Count == 2)
                        {
                            sparqlFunc = new StrEndsFunction(args[0], args[1]);
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL STRENDS() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordStrLang:
                        if (args.Count == 2)
                        {
                            sparqlFunc = new StrLangFunction(args[0], args[1]);
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL STRLANG() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordStrLen:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new StrLenFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL STRKEN() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordStrStarts:
                        if (args.Count == 2)
                        {
                            sparqlFunc = new StrStartsFunction(args[0], args[1]);
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL STRSTARTS() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordSubStr:
                        if (args.Count == 2)
                        {
                            sparqlFunc = new SubStrFunction(args[0], args[1]);
                        }
                        else if (args.Count == 3)
                        {
                            sparqlFunc = new SubStrFunction(args[0], args[1], args[2]);
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL SUBSTR() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordSum:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new AggregateTerm(new SumAggregate(args.First()));
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL SUM() aggregate");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordTimezone:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new TimezoneFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL TIMEZONE() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordTz:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new TZFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL TZ() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordUCase:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new UCaseFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL UCASE() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordUri:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new IriFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL URI() function");
                        }
                        break;
                    case SparqlSpecsHelper.SparqlKeywordYear:
                        if (args.Count == 1)
                        {
                            sparqlFunc = new YearFunction(args.First());
                        }
                        else
                        {
                            throw new RdfParseException("Incorrect number of arguments for the SPARQL YEAR() function");
                        }
                        break;
                }

                if (sparqlFunc != null)
                {
                    expr = sparqlFunc;
                    return true;
                }
            }
            expr = null;
            return false;
        }