Flee allows customization of its expression parser. Customizing the parser is done through the
ExpressionContext.ParserOptions property. You set the properties to the values you want and then call
RecreateParser to apply your changes.
Here's an example:
ExpressionContext context = new ExpressionContext();
context.Imports.AddType(typeof(Math))
context.CompileDynamic("max(1.23, 4.56)", context);
context.ParserOptions.DecimalSeparator = ',';
context.ParserOptions.FunctionArgumentSeparator = ';';
context.RecreateParser();
context.CompileDynamic("max(1,23; 4,56)", context);