如何?但是我需要一个解析器,它只解析一次字符串并且有一个像这样的接口
Func<double,double> MathEvaluator(string input)
或者像这样
LambdaExpression MathEvaluator(string input)
它存在吗?
所以我做了一个库,如果你愿意,你可以使用它,我认为它已经足够好了。有一些正则表达式,将 a^b 之类的结构替换为 Math.Pow(a,b) 等。它可能会更好,但这对我来说很难,但我正在努力。
using System;
using System.CodeDom.Compiler;
using System.IO;
using System.Reflection;
using System.Text.RegularExpressions;
using Microsoft.CSharp;
namespace MathEvalNS
{
public class MathEvaluator
{
private readonly Delegate parsedFunction;
private readonly string normalized;
public double Invoke(double x)
{
if (parsedFunction == null)
throw new NullReferenceException("No function to invoke");
return (double)parsedFunction.DynamicInvoke(x);
}
private const string Begin =
@"using System;
namespace MyNamespace
{
public static class LambdaCreator
{
public static Func<double,double> Create()
{
return (x)=>";
private const string End = @";
}
}
}";
public MathEvaluator(string input)
{
normalized = Normalize(input);
var provider = new CSharpCodeProvider();
var parameters = new CompilerParameters { GenerateInMemory = true };
parameters.ReferencedAssemblies.Add("System.dll");
CompilerResults results = provider.CompileAssemblyFromSource(parameters, Begin + normalized + End);
try
{
var cls = results.CompiledAssembly.GetType("MyNamespace.LambdaCreator");
var method = cls.GetMethod("Create", BindingFlags.Static | BindingFlags.Public);
parsedFunction = (method.Invoke(null, null) as Delegate);
}
catch (FileNotFoundException)
{
throw new ArgumentException();
}
}
private string Normalize(string input)
{
return input.ReplaceMath().ReplacePow().ReplaceMultipling().ReplaceToDoubles();
}
}
public static class StringHelper
{
public static string ReplaceMultipling(this string input)
{
return Regex.Replace(input, @"(\d+)(x)", @"$1*$2");
}
public static string ReplacePow(this string input)
{
var result = input.ReplacePow(@"(\d*x)\^(\d+\.?\d*)");
return result.ReplacePow(@"\(([^\^]+)\)\^(\d+\.?\d*)");
}
private static string ReplacePow(this string input, string toReplace)
{
return Regex.Replace(input, toReplace, "Math.Pow($1,$2)");
}
public static string ReplaceToDoubles(this string input)
{
return Regex.Replace(input, @"(\d+)(?:[^\.]\d+)", "$1.0");
}
public static string ReplaceMath(this string input)
{
return
input.ReplaceMath("sin", @"Math.Sin")
.ReplaceMath("cos", @"Math.Cos")
.ReplaceMath("ctg", @"1.0/Math.Tan")
.ReplaceMath("tg", @"Math.Tan");
}
private static string ReplaceMath(this string input, string name, string dotNetName)
{
return Regex.Replace(input, name, dotNetName, RegexOptions.IgnoreCase);
}
}
}
我有一个 MathParser:http: //github.com/MathewSachin/MathParser
我希望你想要的可以这样完成:
Fuc<double, double> Parse(string Expression)
{
MathParser P = new MathParser();
Variable V = new Variable("x", 0); // The Variable you use with default value
P.Variables.Add(V);
P.Parse(Expression);
return (Input) =>
{
V.Value = Input;
return P.Evaluate();
}
}
我唯一担心的是垃圾收集。