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Evaluating Mathematical Expressions by Compiling C# Code at Runtime

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21 Apr 20032 min read 218.6K   81   23
A completely new way of making a mathematical expression evaluator.

Introduction

There are many articles on creating mathematical expression parsers (i.e. for displaying 3D functions where user inputs the formulas manually). Most of them are based on lexical analysis, grammar definitions etc. With C# there is a solution for making mathematical expression evaluator in a completely new way: by compiling code at runtime.

Let's assume that we want to create an application that would calculate 3D function like that:

z = f(x,y)

But we want to let the user input function formula manually (we don't know what the formula will look like).

A solution to deal with that task in 10 minutes is:

  1. Let the user input the function
  2. Compile that function into memory
  3. Run the function with given x and y
  4. Do something with result z value


To do that in a couple of minutes we would need a class with virtual method:

C#
namespace MathEval<BR>{<BR> public class MyClassBase<BR> {<BR>  public MyClassBase()<BR>  {<BR>  }<BR>  public virtual double eval(double x,double y)<BR>  {<BR>   return 0.0;<BR>  }<BR> }<BR>}<BR>

all we need more is a parser/evaluator class which would compile function body into assembly (created in memory) and calculate function result:

C#
<BR>using System;<BR>using System.Reflection;<BR>using System.Windows.Forms;<BR>namespace MathEval<BR>{<BR> public class MathExpressionParser<BR> {<BR>  MyClassBase myobj = null;<BR>  public MathExpressionParser()<BR>  {<BR>  }<BR>  public bool init(string expr)<BR>  {<BR>   Microsoft.CSharp.CSharpCodeProvider cp<BR>                                = new Microsoft.CSharp.CSharpCodeProvider();<BR>   System.CodeDom.Compiler.ICodeCompiler ic = cp.CreateCompiler();<BR>   System.CodeDom.Compiler.CompilerParameters cpar<BR>                         = new System.CodeDom.Compiler.CompilerParameters();<BR>   cpar.GenerateInMemory = true;<BR>   cpar.GenerateExecutable = false;<BR>   cpar.ReferencedAssemblies.Add("system.dll");<BR>   cpar.ReferencedAssemblies.Add("matheval.exe"); <BR>   string src = "using System;"+<BR>    "class myclass:MathEval.MyClassBase" + <BR>    "{"+<BR>    "public myclass(){}"+<BR>    "public override double eval(double x,double y)"+<BR>    "{"+<BR>    "return "+ expr +";"+<BR>    "}"+<BR>    "}";<BR>   System.CodeDom.Compiler.CompilerResults cr<BR>                                   = ic.CompileAssemblyFromSource(cpar,src);<BR>   foreach (System.CodeDom.Compiler.CompilerError ce in cr.Errors)<BR>    MessageBox.Show(ce.ErrorText); <BR><BR>   if (cr.Errors.Count == 0 && cr.CompiledAssembly != null)<BR>   {<BR>    Type ObjType = cr.CompiledAssembly.GetType("myclass");<BR>    try<BR>    {<BR>     if (ObjType != null)<BR>     {<BR>      myobj = (MyClassBase)Activator.CreateInstance(ObjType);<BR>     }<BR>    }<BR>    catch (Exception ex)<BR>    {<BR>     MessageBox.Show(ex.Message);<BR>    }<BR>    return true;<BR>   }<BR>   else <BR>    return false;<BR>  }<BR>  public double eval(double x,double y)<BR>  {<BR>   double val = 0.0;<BR>   if (myobj != null)<BR>   {<BR>     val = myobj.eval(x,y);<BR>   }<BR>   return val;<BR>  }<BR> }<BR>}<BR>

Take a look at the init() method. All we need it to do is to create an assembly(in memory) with a class "myclass" derived from MyBaseClass. Note that "eval" method contains the formula given by the user at runtime. Also note that cpar.ReferencedAssemblies.Add("matheval.exe"); defines a reference to the application currently being created.
Then we can call myclass.eval method as many times as we want to:

C#
<BR>MathExpressionParser mp = new MathExpressionParser();<BR>mp.init("Math.Sin(x)*y");<BR><BR><BR>for(int i=0;i<1000000;i++)<BR>{<BR> mp.eval((double)i,(double)i);<BR>}<BR>

Compiled code is of course much faster than any other solution used to parse and evaluate expressions.

A few things to do:

  • Let the user input formulas as "xy*sin(x+y)" or "x^2+y^2" and convert them to c# "x*y*Math.Sin(x+y)" "x*x + y*y" etc...
  • Do some error checking/handling other than compiler errors.
  • Freeing and recreating the in-memory-assembly with another formula.
  • Enjoy the code :)

PS: special thanks to AcidRain for some ideas :)

License

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Comments and Discussions

 
QuestionCompile function in memory in objective-c for mac Pin
wonkypuh1018-Jun-11 12:17
wonkypuh1018-Jun-11 12:17 
QuestionCompletely New? Pin
Dewey21-Jan-08 14:28
Dewey21-Jan-08 14:28 
AnswerRe: Completely New? Pin
Marcin Cuprjak23-Jan-08 9:33
Marcin Cuprjak23-Jan-08 9:33 
QuestionWhat is wrong with double FuncN (params double[] x) ? Pin
hreba22-Nov-06 3:40
hreba22-Nov-06 3:40 
GeneralGood Work! Pin
Lutosław3-Oct-06 2:17
Lutosław3-Oct-06 2:17 
GeneralNot applicable for ASP.NET2 applications Pin
ZuZuKin23-Feb-06 9:10
ZuZuKin23-Feb-06 9:10 
GeneralVery Nice Pin
msaroka20-Apr-05 12:48
msaroka20-Apr-05 12:48 
General&quot;matheval.exe&quot; Pin
Noro Korny17-Apr-05 0:11
Noro Korny17-Apr-05 0:11 
GeneralExtremely insecure! Pin
ekolis14-Jun-04 15:59
ekolis14-Jun-04 15:59 
QuestionHow to unload an assembly? Pin
Member 21683830-Jul-03 10:48
Member 21683830-Jul-03 10:48 
AnswerRe: How to unload an assembly? Pin
tuxic7-Mar-05 9:01
tuxic7-Mar-05 9:01 
QuestionWhat about Microsoft.JScript.Eval()? Pin
onc29-Apr-03 3:59
onc29-Apr-03 3:59 
GeneralGenerate IL directly Pin
hsauro22-Apr-03 19:48
hsauro22-Apr-03 19:48 
GeneralRe: Generate IL directly Pin
leppie23-Apr-03 7:02
leppie23-Apr-03 7:02 
Eventually just mapping all the functions to .NET functions and building an evaluation stack would be the fasted.

I rated this article 2 by mistake. It deserves more. I wanted to get to the second page... - vjedlicka 3:33 25 Nov '02
GeneralRe: Generate IL directly Pin
Kris Vandermotten29-Apr-03 4:25
Kris Vandermotten29-Apr-03 4:25 
GeneralCompiling In Memory Pin
Blake Coverett22-Apr-03 16:26
Blake Coverett22-Apr-03 16:26 
GeneralRe: Compiling In Memory Pin
Jonathan de Halleux22-Apr-03 23:02
Jonathan de Halleux22-Apr-03 23:02 
GeneralRe: Compiling In Memory Pin
Rama Krishna Vavilala23-Apr-03 3:12
Rama Krishna Vavilala23-Apr-03 3:12 
GeneralRe: Compiling In Memory Pin
leppie23-Apr-03 7:00
leppie23-Apr-03 7:00 
GeneralRe: Compiling In Memory Pin
Rama Krishna Vavilala23-Apr-03 7:06
Rama Krishna Vavilala23-Apr-03 7:06 
GeneralRe: Compiling In Memory Pin
Blake Coverett23-Apr-03 16:48
Blake Coverett23-Apr-03 16:48 
GeneralRe: Compiling In Memory Pin
Rama Krishna Vavilala24-Apr-03 1:46
Rama Krishna Vavilala24-Apr-03 1:46 
GeneralRe: Compiling In Memory Pin
Blake Coverett24-Apr-03 13:41
Blake Coverett24-Apr-03 13:41 

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