How to implement custom expression

User-defined functions

xFunc supports user-defined functions. The syntax is pretty close to C# lambdas.

To define a function:

f := (x) => sin(x) / cos(x)

where:

• f - is a function name
• := - assign operator
• (x) - the list of parameters of lambda, in this case, x is only one parameter
• => - lambda operator
• sin(x) / cos(x) - the definition of new function (basically tan(x))

After evaluation of this expression, the new function will be added to ExpressionParameters and you will be able to use it in your expressions as any other function:

2 * f(1)

Fork project

I think any possible "real" use case could be handled by User-defined functions. But in case you need something really special to implement, you need to fork the project and implement it by yourself. Please, follow this guide: How to build the project.

To implement a new expression:

• create a new class and implement IExpression (or any other base class, like UnaryExpression, BinaryExpression, etc.)
• modify the Parser.CreateFunction method (in Parser.ExpressionFactory.cs file), so the parser could use your new expression

Old versions of xFunc (before 4.0.0)

The design of old versions was inspired by the ASP.NET MVC framework, where you could replace/extend almost anything. The same was true for xFunc, you could replace/add/extend almost anything (lexer/parser/any expression). So, to add a new expression you needed to implement it in the C# code (by implementing the IExpression interface or any other base class), extend expression factory and add support of new expression to Lexer. The old lexer/parser was based on RPN.

But in xFunc 4.0.0, the lexer, parser and a lot of other staff were rewritten from scratch and all these extension points were removed. So, if you want to implement a custom function you need to use one of the options described above.

Note: All versions < 4.0.0 are deprecated and no longer supported.