Following is the code of this example:<\/p>\n
\r\nusing System;\r\nusing System.Collections.Generic;\r\nusing System.Linq;\r\nusing System.Text;\r\n\r\nnamespace SimpleParser\r\n{\r\n public abstract class Symbol\r\n {\r\n public List ConstituentSymbols { get; set; }\r\n public override string ToString()\r\n {\r\n string s = ConstituentSymbols.Select(ct => ct.ToString()).StringConcatenate();\r\n return s; \r\n }\r\n public Symbol(params Object[] symbols)\r\n {\r\n List ls = new List();\r\n foreach (var item in symbols)\r\n {\r\n if (item is Symbol)\r\n ls.Add((Symbol)item);\r\n else if (item is IEnumerable)\r\n foreach (var item2 in (IEnumerable)item)\r\n ls.Add(item2);\r\n else\r\n \/\/ If this error is thrown, the parser is coded incorrectly.\r\n throw new ParserException(\"Internal error\");\r\n }\r\n ConstituentSymbols = ls;\r\n }\r\n public Symbol() { }\r\n }\r\n\r\n public class Formula : Symbol\r\n {\r\n public static Formula Produce(IEnumerable symbols)\r\n {\r\n \/\/ formula = expression\r\n\r\n Expression e = Expression.Produce(symbols);\r\n return e == null ? null : new Formula(e);\r\n }\r\n public Formula(params Object[] symbols) : base(symbols) { }\r\n }\r\n\r\n public class Expression : Symbol\r\n {\r\n public static Expression Produce(IEnumerable symbols)\r\n {\r\n \/\/ expression = *whitespace nospace-expression *whitespace\r\n\r\n int whiteSpaceBefore = symbols.TakeWhile(s => s is WhiteSpace).Count();\r\n int whiteSpaceAfter = symbols.Reverse().TakeWhile(s => s is WhiteSpace).Count();\r\n IEnumerable noSpaceSymbolList = symbols\r\n .Skip(whiteSpaceBefore)\r\n .SkipLast(whiteSpaceAfter)\r\n .ToList();\r\n NospaceExpression n = NospaceExpression.Produce(noSpaceSymbolList);\r\n if (n != null)\r\n return new Expression(\r\n Enumerable.Repeat(new WhiteSpace(), whiteSpaceBefore),\r\n n,\r\n Enumerable.Repeat(new WhiteSpace(), whiteSpaceAfter));\r\n return null;\r\n }\r\n\r\n public Expression(params Object[] symbols) : base(symbols) { }\r\n }\r\n\r\n public class NospaceExpression : Symbol\r\n {\r\n public static Dictionary OperatorPrecedence = new Dictionary()\r\n {\r\n { \"^\", 3 },\r\n { \"*\", 2 },\r\n { \"\/\", 2 },\r\n { \"+\", 1 },\r\n { \"-\", 1 },\r\n };\r\n\r\n public static NospaceExpression Produce(IEnumerable symbols)\r\n {\r\n \/\/ nospace-expression = open-parenthesis expression close-parenthesis\r\n \/\/ \/ numerical-constant\r\n \/\/ \/ prefix-operator expression\r\n \/\/ \/ expression infix-operator expression\r\n\r\n if (!symbols.Any())\r\n return null;\r\n\r\n if (symbols.First() is OpenParenthesis && symbols.Last() is CloseParenthesis)\r\n {\r\n Expression e = Expression.Produce(symbols.Skip(1).SkipLast(1));\r\n if (e != null)\r\n return new NospaceExpression(new OpenParenthesis(), e, new CloseParenthesis());\r\n }\r\n\r\n \/\/ expression, infix-operator, expression\r\n var z = symbols.Rollup(0, (t, d) =>\r\n {\r\n if (t is OpenParenthesis)\r\n return d + 1;\r\n if (t is CloseParenthesis)\r\n return d - 1;\r\n return d;\r\n });\r\n var symbolsWithIndex = symbols.Select((s, i) => new\r\n {\r\n Symbol = s,\r\n Index = i,\r\n });\r\n var z2 = symbolsWithIndex.Zip(z, (v1, v2) => new\r\n {\r\n SymbolWithIndex = v1,\r\n Depth = v2,\r\n });\r\n var operatorList = z2\r\n .Where(x => x.Depth == 0 &&\r\n x.SymbolWithIndex.Index != 0 &&\r\n InfixOperator.Produce(x.SymbolWithIndex.Symbol) != null)\r\n .ToList();\r\n if (operatorList.Any())\r\n {\r\n int minPrecedence = operatorList\r\n .Select(o2 => OperatorPrecedence[o2.SymbolWithIndex.Symbol.ToString()]).Min();\r\n var op = operatorList\r\n .Last(o2 => OperatorPrecedence[o2.SymbolWithIndex.Symbol.ToString()] == minPrecedence);\r\n if (op != null)\r\n {\r\n var expressionTokenList1 = symbols.TakeWhile(t => t != op.SymbolWithIndex.Symbol);\r\n Expression e1 = Expression.Produce(expressionTokenList1);\r\n if (e1 == null)\r\n throw new ParserException(\"Invalid expression\");\r\n var expressionTokenList2 = symbols\r\n .SkipWhile(t => t != op.SymbolWithIndex.Symbol).Skip(1);\r\n Expression e2 = Expression.Produce(expressionTokenList2);\r\n if (e2 == null)\r\n throw new ParserException(\"Invalid expression\");\r\n InfixOperator io = new InfixOperator(op.SymbolWithIndex.Symbol);\r\n return new NospaceExpression(e1, io, e2);\r\n }\r\n }\r\n\r\n NumericalConstant n = NumericalConstant.Produce(symbols);\r\n if (n != null)\r\n return new NospaceExpression(n);\r\n\r\n PrefixOperator p = PrefixOperator.Produce(symbols.FirstOrDefault());\r\n if (p != null)\r\n {\r\n Expression e = Expression.Produce(symbols.Skip(1));\r\n if (e != null)\r\n return new NospaceExpression(p, e);\r\n }\r\n\r\n return null;\r\n }\r\n\r\n public NospaceExpression(params Object[] symbols) : base(symbols) { }\r\n }\r\n\r\n public class NumericalConstant : Symbol\r\n {\r\n public static NumericalConstant Produce(IEnumerable symbols)\r\n {\r\n \/\/ numerical-constant = [neg-sign] significand-part\r\n\r\n SignificandPart s = SignificandPart.Produce(symbols);\r\n if (s != null)\r\n return new NumericalConstant(s);\r\n NegSign n = NegSign.Produce(symbols.First());\r\n if (n != null)\r\n {\r\n SignificandPart s2 = SignificandPart.Produce(symbols.Skip(1));\r\n if (s2 != null)\r\n return new NumericalConstant(n, s2);\r\n }\r\n return null;\r\n }\r\n public NumericalConstant(params Object[] symbols) : base(symbols) { }\r\n }\r\n\r\n public class SignificandPart : Symbol\r\n {\r\n public static SignificandPart Produce(IEnumerable symbols)\r\n {\r\n \/\/ significand-part = whole-number-part [fractional-part] \/ fractional-part\r\n\r\n FractionalPart f;\r\n f = FractionalPart.Produce(symbols);\r\n if (f != null)\r\n return new SignificandPart(f);\r\n IEnumerable s = null;\r\n WholeNumberPart w = WholeNumberPart.Produce(symbols, out s);\r\n if (w != null)\r\n {\r\n if (!s.Any())\r\n return new SignificandPart(w);\r\n f = FractionalPart.Produce(s);\r\n if (f != null)\r\n return new SignificandPart(w, f);\r\n }\r\n return null;\r\n }\r\n public SignificandPart(params Object[] symbols) : base(symbols) { }\r\n }\r\n\r\n public class WholeNumberPart : Symbol\r\n {\r\n public static WholeNumberPart Produce(IEnumerable symbols,\r\n out IEnumerable symbolsToProcess)\r\n {\r\n \/\/ whole-number-part = digit-sequence\r\n\r\n IEnumerable s = null;\r\n DigitSequence d = DigitSequence.Produce(symbols, out s);\r\n if (d != null)\r\n {\r\n symbolsToProcess = s;\r\n return new WholeNumberPart(d);\r\n }\r\n symbolsToProcess = null;\r\n return null;\r\n }\r\n public WholeNumberPart(params Object[] symbols) : base(symbols) { }\r\n }\r\n\r\n public class FractionalPart : Symbol\r\n {\r\n public static FractionalPart Produce(IEnumerable symbols)\r\n {\r\n \/\/ fractional-part = full-stop digit-sequence\r\n\r\n if (!symbols.Any())\r\n return null;\r\n if (symbols.First() is FullStop)\r\n {\r\n IEnumerable s = null;\r\n DigitSequence d = DigitSequence.Produce(symbols.Skip(1), out s);\r\n if (d == null || s.Any())\r\n return null;\r\n return new FractionalPart(new FullStop(), d);\r\n }\r\n return null;\r\n }\r\n public FractionalPart(params Object[] symbols) : base(symbols) { }\r\n }\r\n\r\n public class DigitSequence : Symbol\r\n {\r\n public static DigitSequence Produce(IEnumerable symbols,\r\n out IEnumerable symbolsToProcess)\r\n {\r\n \/\/ digit-sequence = 1*decimal-digit\r\n\r\n IEnumerable digits = symbols.TakeWhile(s => s is DecimalDigit);\r\n if (digits.Any())\r\n {\r\n symbolsToProcess = symbols.Skip(digits.Count());\r\n return new DigitSequence(digits);\r\n }\r\n symbolsToProcess = null;\r\n return null;\r\n }\r\n public DigitSequence(params Object[] symbols) : base(symbols) { }\r\n }\r\n\r\n public class NegSign : Symbol\r\n {\r\n public static NegSign Produce(Symbol symbol)\r\n {\r\n \/\/ neg-sign = minus\r\n\r\n if (symbol is Minus)\r\n return new NegSign(symbol);\r\n return null;\r\n }\r\n public NegSign(params Object[] symbols) : base(symbols) { }\r\n }\r\n\r\n public class PrefixOperator : Symbol\r\n {\r\n public static PrefixOperator Produce(Symbol symbol)\r\n {\r\n \/\/ prefix-operator = plus \/ minus\r\n\r\n if (symbol is Plus || symbol is Minus)\r\n return new PrefixOperator(symbol);\r\n return null;\r\n }\r\n public PrefixOperator(params Object[] symbols) : base(symbols) { }\r\n }\r\n\r\n public class InfixOperator : Symbol\r\n {\r\n public static InfixOperator Produce(Symbol symbol)\r\n {\r\n \/\/ infix-operator = caret \/ asterisk \/ forward-slash \/ plus \/ minus\r\n\r\n if (symbol is Plus || symbol is Minus || symbol is Asterisk || symbol is ForwardSlash\r\n || symbol is Caret)\r\n return new InfixOperator(symbol);\r\n return null;\r\n }\r\n public InfixOperator(params Object[] symbols) : base(symbols) { }\r\n }\r\n\r\n public class DecimalDigit : Symbol\r\n {\r\n private string CharacterValue;\r\n public override string ToString() { return CharacterValue; }\r\n public DecimalDigit(char c) { CharacterValue = c.ToString(); }\r\n }\r\n\r\n public class WhiteSpace : Symbol\r\n {\r\n public override string ToString() { return \" \"; }\r\n public WhiteSpace() { }\r\n }\r\n\r\n public class Plus : Symbol\r\n {\r\n public override string ToString() { return \"+\"; }\r\n public Plus() { }\r\n }\r\n\r\n public class Minus : Symbol\r\n {\r\n public override string ToString() { return \"-\"; }\r\n public Minus() { }\r\n }\r\n\r\n public class Asterisk : Symbol\r\n {\r\n public override string ToString() { return \"*\"; }\r\n public Asterisk() { }\r\n }\r\n\r\n public class ForwardSlash : Symbol\r\n {\r\n public override string ToString() { return \"\/\"; }\r\n public ForwardSlash() { }\r\n }\r\n\r\n public class Caret : Symbol\r\n {\r\n public override string ToString() { return \"^\"; }\r\n public Caret() { }\r\n }\r\n\r\n public class FullStop : Symbol\r\n {\r\n public override string ToString() { return \".\"; }\r\n public FullStop() { }\r\n }\r\n\r\n public class OpenParenthesis : Symbol\r\n {\r\n public override string ToString() { return \"(\"; }\r\n public OpenParenthesis() { }\r\n }\r\n\r\n public class CloseParenthesis : Symbol\r\n {\r\n public override string ToString() { return \")\"; }\r\n public CloseParenthesis() { }\r\n }\r\n\r\n public class SimpleFormulaParser\r\n {\r\n public static Symbol ParseFormula(string s)\r\n {\r\n IEnumerable symbols = s.Select(c =>\r\n {\r\n switch (c)\r\n {\r\n case '0':\r\n case '1':\r\n case '2':\r\n case '3':\r\n case '4':\r\n case '5':\r\n case '6':\r\n case '7':\r\n case '8':\r\n case '9':\r\n return new DecimalDigit(c);\r\n case ' ':\r\n return new WhiteSpace();\r\n case '+':\r\n return new Plus();\r\n case '-':\r\n return new Minus();\r\n case '*':\r\n return new Asterisk();\r\n case '\/':\r\n return new ForwardSlash();\r\n case '^':\r\n return new Caret();\r\n case '.':\r\n return new FullStop();\r\n case '(':\r\n return new OpenParenthesis();\r\n case ')':\r\n return new CloseParenthesis();\r\n default:\r\n return (Symbol)null;\r\n }\r\n });\r\n#if false\r\n if (symbols.Any())\r\n {\r\n Console.WriteLine(\"Terminal Symbols\");\r\n Console.WriteLine(\"================\");\r\n foreach (var terminal in symbols)\r\n Console.WriteLine(\"{0} >{1}<\", terminal.GetType().Name.ToString(),\r\n terminal.ToString());\r\n Console.WriteLine();\r\n }\r\n#endif\r\n Formula formula = Formula.Produce(symbols);\r\n if (formula == null)\r\n throw new ParserException(\"Invalid formula\");\r\n return formula;\r\n }\r\n\r\n public static void DumpSymbolRecursive(StringBuilder sb, Symbol symbol, int depth)\r\n {\r\n sb.Append(string.Format(\"{0}{1} >{2}<\",\r\n \"\".PadRight(depth * 2),\r\n symbol.GetType().Name.ToString(),\r\n symbol.ToString())).Append(Environment.NewLine);\r\n if (symbol.ConstituentSymbols != null)\r\n foreach (var childSymbol in symbol.ConstituentSymbols)\r\n DumpSymbolRecursive(sb, childSymbol, depth + 1);\r\n }\r\n }\r\n\r\n class Program\r\n {\r\n static void Main(string[] args)\r\n {\r\n string[] sampleValidFormulas = new[] {\r\n \"1+((2+3)*4)^5\",\r\n \"1+2-3*4\/5^6\",\r\n \"(1+2)\/3\",\r\n \" (1+3) \",\r\n \"-123\",\r\n \"1+2*(-3)\",\r\n \"1+2*( - 3)\",\r\n \"12.34\",\r\n \".34\",\r\n \"-123+456\",\r\n \" ( 123 + 456 ) \",\r\n \"-.34\",\r\n \"-12.34\",\r\n \"-(123+456)\",\r\n };\r\n\r\n string[] sampleInvalidFormulas = new[] {\r\n \"-(123+)\",\r\n \"-(*123)\",\r\n \"*123\",\r\n \"*123a\",\r\n \"1.\",\r\n \"--1\",\r\n };\r\n\r\n StringBuilder sb = new StringBuilder();\r\n foreach (var formula in sampleValidFormulas)\r\n {\r\n Symbol f = SimpleFormulaParser.ParseFormula(formula);\r\n SimpleFormulaParser.DumpSymbolRecursive(sb, f, 0);\r\n sb.Append(\"==================================\" + Environment.NewLine);\r\n }\r\n foreach (var formula in sampleInvalidFormulas)\r\n {\r\n bool exceptionThrown = false;\r\n try\r\n {\r\n Symbol f = SimpleFormulaParser.ParseFormula(formula);\r\n }\r\n catch (ParserException e)\r\n {\r\n exceptionThrown = true;\r\n sb.Append(String.Format(\"Parsing >{0}< Exception: {1}\", formula, e.Message) +\r\n Environment.NewLine);\r\n }\r\n if (!exceptionThrown)\r\n sb.Append(String.Format(\"Parsing >{0}< Should have thrown exception, but did not\",\r\n formula) + Environment.NewLine);\r\n }\r\n Console.WriteLine(sb.ToString());\r\n }\r\n }\r\n\r\n public class ParserException : Exception\r\n {\r\n public ParserException(string message) : base(message) { }\r\n }\r\n\r\n public static class MyExtensions\r\n {\r\n public static IEnumerable SkipLast(this IEnumerable source,\r\n int count)\r\n {\r\n Queue saveList = new Queue();\r\n int saved = 0;\r\n foreach (T item in source)\r\n {\r\n if (saved < count)\r\n {\r\n saveList.Enqueue(item);\r\n ++saved;\r\n continue;\r\n }\r\n saveList.Enqueue(item);\r\n yield return saveList.Dequeue();\r\n }\r\n yield break;\r\n }\r\n\r\n public static string StringConcatenate(this IEnumerable source)\r\n {\r\n StringBuilder sb = new StringBuilder();\r\n foreach (string s in source)\r\n sb.Append(s);\r\n return sb.ToString();\r\n }\r\n\r\n public static string StringConcatenate(\r\n this IEnumerable source,\r\n Func projectionFunc)\r\n {\r\n return source.Aggregate(new StringBuilder(),\r\n (s, i) => s.Append(projectionFunc(i)),\r\n s => s.ToString());\r\n }\r\n\r\n public static IEnumerable Rollup(\r\n this IEnumerable source,\r\n TResult seed,\r\n Func projection)\r\n {\r\n TResult nextSeed = seed;\r\n foreach (TSource src in source)\r\n {\r\n TResult projectedValue = projection(src, nextSeed);\r\n nextSeed = projectedValue;\r\n yield return projectedValue;\r\n }\r\n }\r\n }\r\n}\r\n<\/pre>\n","protected":false},"excerpt":{"rendered":"Following is the code of this example: using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace SimpleParser { public abstract class Symbol { public List ConstituentSymbols { get; set; } public override string ToString() { string s = ConstituentSymbols.Select(ct => ct.ToString()).StringConcatenate(); return s; } public Symbol(params Object[] symbols) { List ls = new List(); foreach 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