Flee Customizing Parser

The Flee library allows you to customize the expression parser.

• You can use the ExpressionContext.ParserOptions property to customize the parser.
• You set the properties to the values you want and then call RecreateParser to apply your changes.

Let's consider the following simple example with the default settings.

public static void Example1()
{
    ExpressionContext context = new ExpressionContext();
    context.Imports.AddType(typeof(Math));

    string expression = "Min(2.50, 4.75)";
    var eDynamic = context.CompileDynamic(expression);

    var result = eDynamic.Evaluate();
    Console.WriteLine("{0} = {1}", expression, result);
}

Let's execute the above code, and you will see the following output.

Min(2.50, 4.75) = 2.5

Now let's say we want to use comma (,) instead of dot (.) as a decimal separator, and use semicolon (;) instead of a comma (,) as an argument separator.

public static void Example2()
{
    ExpressionContext context = new ExpressionContext();
    context.Imports.AddType(typeof(Math));

    context.ParserOptions.DecimalSeparator = ',';
    context.ParserOptions.FunctionArgumentSeparator = ';';
    context.ParserOptions.RecreateParser();

    var expression = "Min(2,50; 4,75)";
    var eDynamic = context.CompileDynamic(expression);

    var result = eDynamic.Evaluate();
    Console.WriteLine("{0} = {1}", expression, result);
}

Let's execute the above code, and you will see the following output.

Min(2,50; 4,75) = 2.5