Expression<Func<int, bool>> lambda = num => num < 5; 

ParameterExpression numPara = Expression.Parameter(typeof(int), "num");//參數(shù)num
ConstantExpression five = Expression.Constant(5, typeof(int));//常數(shù)5

BinaryExpression numLessThanFive = Expression.LessThan(numPara, five);
Expression<Func<int, bool>> lambda1 = Expression.Lambda<Func<int, bool>>(numLessThanFive, new ParameterExpression[] { numPara });

//參數(shù)value
ParameterExpression value = Expression.Parameter(typeof(int), "value");
//本地變量
ParameterExpression result = Expression.Parameter(typeof(int), "result");
//標(biāo)簽，用來(lái)跳出循環(huán)
LabelTarget label = Expression.Label(typeof(int));
//創(chuàng)建表達(dá)式塊
BlockExpression block = Expression.Block(
 //添加本地參數(shù)result
 new[] { result },
 //result=1 賦值
 Expression.Assign(result, Expression.Constant(1)),
 //循環(huán)
 Expression.Loop(
  //循環(huán)條件
  Expression.IfThenElse(
   //如果 value>1
   Expression.GreaterThan(value, Expression.Constant(1)),
   //則 result*=value--;
   Expression.MultiplyAssign(result, Expression.PostDecrementAssign(value)),
   //否則跳出loop循環(huán)。跳到label的語(yǔ)句執(zhí)行
   Expression.Break(label, result)
   ),
   label
  )
);
//編譯表達(dá)式樹(shù)
Func<int, int> factor = Expression.Lambda<Func<int, int>>(block, value).Compile();
//執(zhí)行，輸出結(jié)果120
Console.WriteLine(factor(5));

Expression<Func<int, bool>> expreTree = num => num < 5;

ParameterExpression param = (ParameterExpression)expreTree.Parameters[0];//num
BinaryExpression operation = (BinaryExpression)expreTree.Body;//<
ParameterExpression left = (ParameterExpression)operation.Left;//num
ConstantExpression right = (ConstantExpression)operation.Right;//5
                //output Decomposed expression: num => num LessThan 5 
Console.WriteLine("Decomposed expression:{0} = > {1} {2} {3}", param.Name, left.Name, operation.NodeType, right.Value);

// 創(chuàng)建表達(dá)式樹(shù)
Expression<Func<int, bool>> expr = num => num < 5;
// 將表達(dá)式樹(shù)編譯成對(duì)應(yīng)委托 
Func<int, bool> result = expr.Compile();
//調(diào)用委托方法，輸出True
Console.WriteLine(result(4));
//也可以直接編譯后調(diào)用，輸出True
Console.WriteLine(expr.Compile()(4));

//創(chuàng)建表達(dá)式樹(shù)的執(zhí)行邏輯
BinaryExpression be = Expression.Power(Expression.Constant(2D), Expression.Constant(3D));
//創(chuàng)建表達(dá)式樹(shù)
Expression<Func<double>> le = Expression.Lambda<Func<double>>(be);
//編譯表達(dá)式樹(shù)
Func<double> compileExpression = le.Compile();
//執(zhí)行l(wèi)ambda表達(dá)式,獲得結(jié)果8
double result = compileExpression();
Console.WriteLine(result);