Linq表达式树解析1

浅浅的花香味﹌ 2022-08-13 06:58 189阅读 0赞

原文：[http://www.codeproject.com/Articles/355513/Invent-your-own-Dynamic-LINQ-parser][http_www.codeproject.com_Articles_355513_Invent-your-own-Dynamic-LINQ-parser]

LINQ Expression Tree

*  LINQ Expression Tree: [http://msdn.microsoft.com/en-us/library/bb397951.aspx][http_msdn.microsoft.com_en-us_library_bb397951.aspx]
 *  LINQ Expressions: [http://msdn.microsoft.com/en-us/library/system.linq.expressions.aspx][http_msdn.microsoft.com_en-us_library_system.linq.expressions.aspx]
 *  Expression Factory: [http://msdn.microsoft.com/en-us/library/system.linq.expressions.expression.aspx][http_msdn.microsoft.com_en-us_library_system.linq.expressions.expression.aspx]

Dynamic LINQ

*  ScottGu's Blog [http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx][http_weblogs.asp.net_scottgu_archive_2008_01_07_dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx]

核心代码：

using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Linq.Expressions;
    using System.Text.RegularExpressions;
    
    namespace SimpleExpression
    {
        public abstract class PredicateParser
        {
            #region scanner
            /// <summary>tokenizer pattern: Optional-SpaceS...Token...Optional-Spaces</summary>
            private static readonly string _pattern = @"\s*(" + string.Join("|", new string[]
              {
                  // operators and punctuation that are longer than one char: longest first
                  string.Join("|", new string[] { "||", "&&", "==", "!=", "<=", ">=" }.Select(e => Regex.Escape(e))),
                  @"""(?:\\.|[^""])*""",  // string
                  @"\d+(?:\.\d+)?",       // number with optional decimal part
                  @"\w+",                 // word
                  @"\S",                  // other 1-char tokens (or eat up one character in case of an error)
              }) + @")\s*";
            /// <summary>get 1st char of current token (or a Space if no 1st char is obtained)</summary>
            private char Ch { get { return string.IsNullOrEmpty(Curr) ? ' ' : Curr[0]; } }
            /// <summary>move one token ahead</summary><returns>true = moved ahead, false = end of stream</returns>
            private bool Move() { return _tokens.MoveNext(); }
            /// <summary>the token stream implemented as IEnumerator<string></summary>
            private IEnumerator<string> _tokens;
            /// <summary>constructs the scanner for the given input string</summary>
            protected PredicateParser(string s)
            {
                _tokens = Regex.Matches(s, _pattern, RegexOptions.Compiled).Cast<Match>()
                          .Select(m => m.Groups[1].Value).GetEnumerator();
                Move();
            }
            protected bool IsNumber { get { return char.IsNumber(Ch); } }
            protected bool IsDouble { get { return IsNumber && Curr.Contains('.'); } }
            protected bool IsString { get { return Ch == '"'; } }
            protected bool IsIdent { get { char c = Ch; return char.IsLower(c) || char.IsUpper(c) || c == '_'; } }
            /// <summary>throw an argument exception</summary>
            protected void Abort(string msg) { throw new ArgumentException("Error: " + (msg ?? "unknown error")); }
            /// <summary>get the current item of the stream or an empty string after the end</summary>
            protected string Curr { get { return _tokens.Current ?? string.Empty; } }
            /// <summary>get current and move to the next token (error if at end of stream)</summary>
            protected string CurrAndNext { get { string s = Curr; if (!Move()) Abort("data expected"); return s; } }
            /// <summary>get current and move to the next token if available</summary>
            protected string CurrOptNext { get { string s = Curr; Move(); return s; } }
            /// <summary>moves forward if current token matches and returns that (next token must exist)</summary>
            protected string CurrOpAndNext(params string[] ops)
            {
                string s = ops.Contains(Curr) ? Curr : null;
                if (s != null && !Move()) Abort("data expected");
                return s;
            }
            #endregion
        }
        public class PredicateParser<TData> : PredicateParser
        {
            #region code generator
    
            private static readonly Type _bool = typeof(bool);
            private static readonly Type[] _prom = new Type[]
            { 
                typeof(decimal), typeof(double), typeof(float), 
                typeof(ulong), typeof(long), typeof(uint),
                typeof(int), typeof(ushort), typeof(char),
                typeof(short), typeof(byte), typeof(sbyte)
            };
    
            /// <summary>enforce the type on the expression (by a cast) if not already of that type</summary>
            private static Expression Coerce(Expression expr, Type type)
            {
                return expr.Type == type ? expr : Expression.Convert(expr, type);
            }
    
            /// <summary>casts if needed the expr to the "largest" type of both arguments</summary>
            private static Expression Coerce(Expression expr, Expression sibling)
            {
                if (expr.Type != sibling.Type)
                {
                    Type maxType = MaxType(expr.Type, sibling.Type);
                    if (maxType != expr.Type) expr = Expression.Convert(expr, maxType);
                }
                return expr;
            }
    
            /// <summary>returns the first if both are same, or the largest type of both (or the first)</summary>
            private static Type MaxType(Type a, Type b)
            {
                return a == b ? a : (_prom.FirstOrDefault(t => t == a || t == b) ?? a);
            }
            /// <summary>
            /// Code generation of binary and unary epressions, utilizing type coercion where needed
            /// </summary>
            private static readonly Dictionary<string, Func<Expression, Expression, Expression>> _binOp =
            new Dictionary<string, Func<Expression, Expression, Expression>>()
            {
                { "||", (a,b)=>Expression.OrElse(Coerce(a, _bool), Coerce(b, _bool)) },
                { "&&", (a,b)=>Expression.AndAlso(Coerce(a, _bool), Coerce(b, _bool)) },
                { "==", (a,b)=>Expression.Equal(Coerce(a,b), Coerce(b,a)) },
                { "!=", (a,b)=>Expression.NotEqual(Coerce(a,b), Coerce(b,a)) },
                { "<", (a,b)=>Expression.LessThan(Coerce(a,b), Coerce(b,a)) },
                { "<=", (a,b)=>Expression.LessThanOrEqual(Coerce(a,b), Coerce(b,a)) },
                { ">=", (a,b)=>Expression.GreaterThanOrEqual(Coerce(a,b), Coerce(b,a)) },
                { ">", (a,b)=>Expression.GreaterThan(Coerce(a,b), Coerce(b,a)) },
            };
    
            private static readonly Dictionary<string, Func<Expression, Expression>> _unOp =
            new Dictionary<string, Func<Expression, Expression>>()
            {
                { "!", a=>Expression.Not(Coerce(a, _bool)) },
            };
    
            /// <summary>create a constant of a value</summary>
            private static ConstantExpression Const(object v) { return Expression.Constant(v); }
            /// <summary>create lambda parameter field or property access</summary>
            private MemberExpression ParameterMember(string s) { return Expression.PropertyOrField(_param, s); }
            /// <summary>create lambda expression</summary>
            private Expression<Func<TData, bool>> Lambda(Expression expr) { return Expression.Lambda<Func<TData, bool>>(expr, _param); }
            /// <summary>the lambda's parameter (all names are members of this)</summary>
            private readonly ParameterExpression _param = Expression.Parameter(typeof(TData), "_p_");
            #endregion
    
            #region parser
            /// <summary>initialize the parser (and thus, the scanner)</summary>
            private PredicateParser(string s) : base(s) { }
            /// <summary>main entry point</summary>
            public static Expression<Func<TData, bool>> Parse(string s) { return new PredicateParser<TData>(s).Parse(); }
            private Expression<Func<TData, bool>> Parse() { return Lambda(ParseExpression()); }
            private Expression ParseExpression() { return ParseOr(); }
            private Expression ParseOr() { return ParseBinary(ParseAnd, "||"); }
            private Expression ParseAnd() { return ParseBinary(ParseEquality, "&&"); }
            private Expression ParseEquality() { return ParseBinary(ParseRelation, "==", "!="); }
            private Expression ParseRelation() { return ParseBinary(ParseUnary, "<", "<=", ">=", ">"); }
            private Expression ParseUnary()
            {
                return CurrOpAndNext("!") != null ? _unOp["!"](ParseUnary()) : ParsePrimary();
            }
            //private Expression ParseIdent() { return ParameterMember(CurrOptNext); } //不支持嵌套
            private Expression ParseIdent() //修改支持嵌套
            {
                Expression expr = ParameterMember(CurrOptNext);
                while (CurrOpAndNext(".") != null && IsIdent) expr = Expression.PropertyOrField(expr, CurrOptNext);
                return expr;
            }
            private Expression ParseString()
            {
                return Const(Regex.Replace(CurrOptNext, "^\"(.*)\"$", m => m.Groups[1].Value));
            }
            private Expression ParseNumber()
            {
                if (IsDouble) return Const(double.Parse(CurrOptNext));
                return Const(int.Parse(CurrOptNext));
            }
            private Expression ParsePrimary()
            {
                if (IsIdent) return ParseIdent();
                if (IsString) return ParseString();
                if (IsNumber) return ParseNumber();
                return ParseNested();
            }
            private Expression ParseNested()
            {
                if (CurrAndNext != "(") Abort("(...) expected");
                Expression expr = ParseExpression();
                if (CurrOptNext != ")") Abort("')' expected");
                return expr;
            }
            /// <summary>generic parsing of binary expressions</summary>
            private Expression ParseBinary(Func<Expression> parse, params string[] ops)
            {
                Expression expr = parse();
                string op;
                while ((op = CurrOpAndNext(ops)) != null) expr = _binOp[op](expr, parse());
                return expr;
            }
            #endregion
        }
    }

测试代码：

using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Linq.Expressions;
    using System.Text.RegularExpressions;
    
    namespace SimpleExpression
    {
        public abstract class PredicateParser
        {
            #region scanner
            /// <summary>tokenizer pattern: Optional-SpaceS...Token...Optional-Spaces</summary>
            private static readonly string _pattern = @"\s*(" + string.Join("|", new string[]
              {
                  // operators and punctuation that are longer than one char: longest first
                  string.Join("|", new string[] { "||", "&&", "==", "!=", "<=", ">=" }.Select(e => Regex.Escape(e))),
                  @"""(?:\\.|[^""])*""",  // string
                  @"\d+(?:\.\d+)?",       // number with optional decimal part
                  @"\w+",                 // word
                  @"\S",                  // other 1-char tokens (or eat up one character in case of an error)
              }) + @")\s*";
            /// <summary>get 1st char of current token (or a Space if no 1st char is obtained)</summary>
            private char Ch { get { return string.IsNullOrEmpty(Curr) ? ' ' : Curr[0]; } }
            /// <summary>move one token ahead</summary><returns>true = moved ahead, false = end of stream</returns>
            private bool Move() { return _tokens.MoveNext(); }
            /// <summary>the token stream implemented as IEnumerator<string></summary>
            private IEnumerator<string> _tokens;
            /// <summary>constructs the scanner for the given input string</summary>
            protected PredicateParser(string s)
            {
                _tokens = Regex.Matches(s, _pattern, RegexOptions.Compiled)
                            .Cast<Match>()
                            .Select(m => m.Groups[1].Value)
                            .GetEnumerator();
                Move();
            }
            protected bool IsNumber { get { return char.IsNumber(Ch); } }
            protected bool IsDouble { get { return IsNumber && Curr.Contains('.'); } }
            protected bool IsString { get { return Ch == '"'; } }
            protected bool IsIdent { get { char c = Ch; return char.IsLower(c) || char.IsUpper(c) || c == '_'; } }
            /// <summary>throw an argument exception</summary>
            protected void Abort(string msg) { throw new ArgumentException("Error: " + (msg ?? "unknown error")); }
            /// <summary>get the current item of the stream or an empty string after the end</summary>
            protected string Curr { get { return _tokens.Current ?? string.Empty; } }
            /// <summary>get current and move to the next token (error if at end of stream)</summary>
            protected string CurrAndNext { get { string s = Curr; if (!Move()) Abort("data expected"); return s; } }
            /// <summary>get current and move to the next token if available</summary>
            protected string CurrOptNext { get { string s = Curr; Move(); return s; } }
            /// <summary>moves forward if current token matches and returns that (next token must exist)</summary>
            protected string CurrOpAndNext(params string[] ops)
            {
                string s = ops.Contains(Curr) ? Curr : null;
                if (s != null && !Move()) Abort("data expected");
                return s;
            }
            #endregion
        }
        public class PredicateParser<TData> : PredicateParser
        {
            #region code generator
            private static readonly Expression _zero = Expression.Constant(0); //add
            private static readonly Type _bool = typeof(bool);
            private static readonly Type[] _prom = new Type[]
            { 
                typeof(decimal), typeof(double), typeof(float), 
                typeof(ulong), typeof(long), typeof(uint),
                typeof(int), typeof(ushort), typeof(char),
                typeof(short), typeof(byte), typeof(sbyte)
            };
    
            /// <summary>enforce the type on the expression (by a cast) if not already of that type</summary>
            private static Expression Coerce(Expression expr, Type type)
            {
                return expr.Type == type ? expr : Expression.Convert(expr, type);
            }
    
            /// <summary>casts if needed the expr to the "largest" type of both arguments</summary>
            private static Expression Coerce(Expression expr, Expression sibling)
            {
                if (expr.Type != sibling.Type)
                {
                    Type maxType = MaxType(expr.Type, sibling.Type);
                    if (maxType != expr.Type) expr = Expression.Convert(expr, maxType);
                }
                return expr;
            }
    
            /// <summary>returns the first if both are same, or the largest type of both (or the first)</summary>
            private static Type MaxType(Type a, Type b)
            {
                return a == b ? a : (_prom.FirstOrDefault(t => t == a || t == b) ?? a);
            }
    
            /// <summary>produce comparison based on IComparable types</summary>
            private static Expression CompareToExpression(Expression lhs, Expression rhs, Func<Expression, Expression> rel)
            {
                lhs = Coerce(lhs, rhs);
                rhs = Coerce(rhs, lhs);
                Expression cmp = Expression.Call(
                    lhs,
                    lhs.Type.GetMethod("CompareTo", new Type[] { rhs.Type })
                        ?? lhs.Type.GetMethod("CompareTo", new Type[] { typeof(object) }),
                    rhs
                );
                return rel(cmp);
            }
    
            /// <summary>
            /// Code generation of binary and unary epressions, utilizing type coercion where needed
            /// </summary>
            private static readonly Dictionary<string, Func<Expression, Expression, Expression>> _binOp =
            new Dictionary<string, Func<Expression, Expression, Expression>>()
            {
                { "||", (a,b)=>Expression.OrElse(Coerce(a, _bool), Coerce(b, _bool)) },
                { "&&", (a,b)=>Expression.AndAlso(Coerce(a, _bool), Coerce(b, _bool)) },
                //{ "==", (a,b)=>Expression.Equal(Coerce(a,b), Coerce(b,a)) },
                //{ "!=", (a,b)=>Expression.NotEqual(Coerce(a,b), Coerce(b,a)) },
                //{ "<", (a,b)=>Expression.LessThan(Coerce(a,b), Coerce(b,a)) },
                //{ "<=", (a,b)=>Expression.LessThanOrEqual(Coerce(a,b), Coerce(b,a)) },
                //{ ">=", (a,b)=>Expression.GreaterThanOrEqual(Coerce(a,b), Coerce(b,a)) },
                //{ ">", (a,b)=>Expression.GreaterThan(Coerce(a,b), Coerce(b,a)) },
                //Replace to=>
                { "==", (a,b)=>CompareToExpression(a, b, c=>Expression.Equal             (c, _zero)) },
                { "!=", (a,b)=>CompareToExpression(a, b, c=>Expression.NotEqual          (c, _zero)) },
                { "<",  (a,b)=>CompareToExpression(a, b, c=>Expression.LessThan          (c, _zero)) },
                { "<=", (a,b)=>CompareToExpression(a, b, c=>Expression.LessThanOrEqual   (c, _zero)) },
                { ">=", (a,b)=>CompareToExpression(a, b, c=>Expression.GreaterThanOrEqual(c, _zero)) },
                { ">",  (a,b)=>CompareToExpression(a, b, c=>Expression.GreaterThan       (c, _zero)) },    
                //To extend the parser=>
                { "+", (a,b)=>Expression.Add(Coerce(a,b), Coerce(b,a)) },
                { "-", (a,b)=>Expression.Subtract(Coerce(a,b), Coerce(b,a)) },
                { "*", (a,b)=>Expression.Multiply(Coerce(a,b), Coerce(b,a)) },
                { "/", (a,b)=>Expression.Divide(Coerce(a,b), Coerce(b,a)) },
                { "%", (a,b)=>Expression.Modulo(Coerce(a,b), Coerce(b,a)) },
            };
    
            private static readonly Dictionary<string, Func<Expression, Expression>> _unOp =
            new Dictionary<string, Func<Expression, Expression>>()
            {
                { "!", a=>Expression.Not(Coerce(a, _bool)) },
                //To extend the parser=>
                { "-", a=>Expression.Negate(a) },
            };
    
            /// <summary>create a constant of a value</summary>
            private static ConstantExpression Const(object v) { return Expression.Constant(v); }
            /// <summary>create lambda parameter field or property access</summary>
            private MemberExpression ParameterMember(string s) { return Expression.PropertyOrField(_param, s); }
            /// <summary>create lambda expression</summary>
            private Expression<Func<TData, bool>> Lambda(Expression expr) { return Expression.Lambda<Func<TData, bool>>(expr, _param); }
            /// <summary>the lambda's parameter (all names are members of this)</summary>
            private readonly ParameterExpression _param = Expression.Parameter(typeof(TData), "_p_");
            #endregion
    
            #region parser
            /// <summary>initialize the parser (and thus, the scanner)</summary>
            private PredicateParser(string s) : base(s) { }
            /// <summary>main entry point</summary>
            public static Expression<Func<TData, bool>> Parse(string s) { return new PredicateParser<TData>(s).Parse(); }
            private Expression<Func<TData, bool>> Parse() { return Lambda(ParseExpression()); }
            private Expression ParseExpression() { return ParseOr(); }
            private Expression ParseOr() { return ParseBinary(ParseAnd, "||"); }
            private Expression ParseAnd() { return ParseBinary(ParseEquality, "&&"); }
            private Expression ParseEquality() { return ParseBinary(ParseRelation, "==", "!="); }
            //private Expression ParseRelation() { return ParseBinary(ParseUnary, "<", "<=", ">=", ">"); }
            private Expression ParseRelation() { return ParseBinary(ParseSum, "<", "<=", ">=", ">"); }
            private Expression ParseSum() { return ParseBinary(ParseMul, "+", "-"); }
            private Expression ParseMul() { return ParseBinary(ParseUnary, "*", "/", "%"); }
    
            private Expression ParseUnary()
            {
                if (CurrOpAndNext("!") != null) return _unOp["!"](ParseUnary());
                if (CurrOpAndNext("-") != null) return _unOp["-"](ParseUnary());
                return ParsePrimary();
                //return CurrOpAndNext("!") != null ? _unOp["!"](ParseUnary()) : ParsePrimary();
            }
            //private Expression ParseIdent() { return ParameterMember(CurrOptNext); } //不支持嵌套
            private Expression ParseIdent() //修改支持嵌套
            {
                Expression expr = ParameterMember(CurrOptNext);
                while (CurrOpAndNext(".") != null && IsIdent) expr = Expression.PropertyOrField(expr, CurrOptNext);
                return expr;
            }
            private Expression ParseString()
            {
                return Const(Regex.Replace(CurrOptNext, "^\"(.*)\"$", m => m.Groups[1].Value));
            }
            private Expression ParseNumber()
            {
                if (IsDouble) return Const(double.Parse(CurrOptNext));
                return Const(int.Parse(CurrOptNext));
            }
            private Expression ParsePrimary()
            {
                if (IsIdent) return ParseIdent();
                if (IsString) return ParseString();
                if (IsNumber) return ParseNumber();
                return ParseNested();
            }
            private Expression ParseNested()
            {
                if (CurrAndNext != "(") Abort("(...) expected");
                Expression expr = ParseExpression();
                if (CurrOptNext != ")") Abort("')' expected");
                return expr;
            }
            /// <summary>generic parsing of binary expressions</summary>
            private Expression ParseBinary(Func<Expression> parse, params string[] ops)
            {
                Expression expr = parse();
                string op;
                while ((op = CurrOpAndNext(ops)) != null) expr = _binOp[op](expr, parse());
                return expr;
            }
            #endregion
        }
    }

测试代码：

using System;
    using System.Collections.Generic;
    using System.Linq;
    
    namespace LinqExpTest
    {
        /// <summary>
        /// Linq 表达式树 测试
        /// </summary>
        class Program
        {
            static void Main(string[] args)
            {
                var items = new List<Element>()
                {
    #region
                    //new Element("a", 1000,new List<CC>{new CC{email="fdsf@fd",age=12}}),
                    //new Element("b", 900,new List<CC>{new CC{email="fdsf@fd",age=12}}),
                    //new Element("c", 800,new List<CC>{new CC{email="fdsf@fd",age=12}}),
                    //new Element("d", 700,new List<CC>{new CC{email="fdsf@fd",age=12}}),
                    //new Element("e", 600,new List<CC>{new CC{email="fdsf@fd",age=12}}),
                    //new Element("x", 500,new List<CC>{new CC{email="fdsf@fd",age=12}}),
                    //new Element("y", 400,new List<CC>{new CC{email="fdsf@fd",age=12}}),
                    //new Element("z", 300,new List<CC>{new CC{email="fdsf@fd",age=12}})
    #endregion
                    new Element("a", 1000,new CC{email="fdsf@fd",age=12}),
                    new Element("b", 900,new CC{email="fdsf@fd",age=17}),
                    new Element("c", 800,new CC{email="fdsf@fd",age=25}),
                    new Element("d", 700,new CC{email="fdsf@fd",age=8}),
                    new Element("e", 600,new CC{email="fdsf@fd",age=9}),
                    new Element("x", 500,new CC{email="fdsf@fd",age=35}),
                    new Element("y", 400,new CC{email="fdsf@fd",age=23}),
                    new Element("z", 900,new CC{email="fdsf@fd",age=16})
                };
    
                //string s = "Name == \"x\" || Number >= 800 && PCC.age % 2==0 && PCC.age>15 && PCC.age*2<35";
                string s = "Name == \"x\" || Number >= 800 && PCC.age>15 && PCC.age*2<35";
                var pred = SimpleExpression.PredicateParser<Element>.Parse(s);
                Console.WriteLine("User Entry: {0}", s);
                Console.WriteLine("Expr Tree:  {0}", pred.ToString());
    
                var f = pred.Compile();
                Console.WriteLine("\r\n==============mark affected items==============");
                foreach (var item in items)
                {
                    Console.WriteLine("{2} Name = {0}, Number = {1}, CC: email={3}, age={4}"
                        , item.Name, item.Number, f(item) ? "x" : " ", item.PCC.email, item.PCC.age);
                }
                Console.WriteLine("==============where-select==============");
                var q = from e in items where f(e) select e;
                foreach (var item in q)
                {
                    Console.WriteLine("  Name = {0}, Number = {1},CC: email={2}, age={3}",
                        item.Name, item.Number, item.PCC.email, item.PCC.age);
                }
    
                Console.ReadKey();
            }
        }
    
        class Element
        {
            private string _name;
            private int _number;
            private CC _cc;
            //private IList<CC> _listcc;
            //public Element(string name, int number, List<CC> listcc)
            public Element(string name, int number, CC cc)
            {
                this._name = name;
                this._number = number;
                this._cc = cc;
                //this._listcc = listcc;
            }
    
            public string Name { get { return _name; } set { _name = value; } }
            public int Number { get { return _number; } set { _number = value; } }
            public CC PCC { get { return _cc; } set { _cc = value; } }
            //public IList<CC> ListCC { get { return _listcc; } set { _listcc = value; } }
        }
        class CC
        {
            public string email { get; set; }
            public int age { get; set; }
        }
    }

输出结果：  
![SouthEast][]

string s = "Name == \"x\" || Number >= 800 && PCC.age % 2==0 && PCC.age>15 && PCC.age*2<35";

![SouthEast 1][]

原文下面提出了对此方法的扩展说明：

Add more operations

To extend the parser: You may easily add more to the expressions, especially new operators is a simple thing:

*  to add `+` and `-` binary operators, add them to the `_binOp `dictionary (similar to `==`, e.g. , (`"+":``Expression.Add(...)`, `"-":` `Expression.Subtract(...)`) create `ParseSum() `as a copy of`ParseRelation`, pass `"+", "-" `as ops, pass `ParseSum `to `ParseRelation `(in place of the `ParseUnary`), pass `ParseUnary `to `ParseSum`. That's it.
 *  likewise for `"*", "/", "%"`: make `ParseMul `as copy of the above mentioned `ParseSum`, pass the right`ParseXXX `actions, add the respective Expression factories to the `_binOps `dictionary. Done.
 *  An unary `"-"` is to be added in the `_unOps `dictionary (no coercion needed). The parsing is done in the`ParseUnary()` function, e.g.

......

[http_www.codeproject.com_Articles_355513_Invent-your-own-Dynamic-LINQ-parser]: http://www.codeproject.com/Articles/355513/Invent-your-own-Dynamic-LINQ-parser
[http_msdn.microsoft.com_en-us_library_bb397951.aspx]: http://msdn.microsoft.com/en-us/library/bb397951.aspx
[http_msdn.microsoft.com_en-us_library_system.linq.expressions.aspx]: http://msdn.microsoft.com/en-us/library/system.linq.expressions.aspx
[http_msdn.microsoft.com_en-us_library_system.linq.expressions.expression.aspx]: http://msdn.microsoft.com/en-us/library/system.linq.expressions.expression.aspx
[http_weblogs.asp.net_scottgu_archive_2008_01_07_dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx]: http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx
[SouthEast]: /images/20220810/0092775075ff4de5a83a5c5cb94a0260.png
[SouthEast 1]: /images/20220810/a6191c27e47b4bf0a5acb4f2123e1f0d.png