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Evaluating an expression

It is sometimes convenient to evaluate a script expression without rendering it to a string.

First, there is an option in TemplateContext.EnableOutput that can be set to disable the output to the TemplateContext.Output StringBuilder.

Also, as in the Abstract Syntax Tree section, all AST ScriptNode have an Evaluate method that returns the result of an evaluation.

Lastly, you can use the convenient static method Template.Evaluate to quickly evaluate an expression relative to a TemplateContext:

var scriptObject1 = new ScriptObject();
scriptObject1.Add("var1", 5);

var context = new TemplateContext();
context.PushGlobal(scriptObject1);

var result = Template.Evaluate("var1 * 5 + 2", context);
// Prints `27`
Console.WriteLine(result);

When using Template.Evaluate, the underlying code will use the ScriptMode.ScriptOnly when compiling the expression and will disable the output on the TemplateContext.

Changing the Culture

The default culture when running a template is CultureInfo.InvariantCulture

You can change the culture that is used when rendering numbers/date/time and parsing date/time by pushing a new Culture to a TemplateContext

var context = new TemplateContext();
context.PushCulture(CultureInfo.CurrentCulture);
// ...
context.PopCulture();

Notice that the parsing of numbers in the language is not culture dependent but is baked into the language specs instead.

Safe Runtime

The TemplateContext provides a few properties to control the runtime and make it safer. You can tweak the following properties:

  • LoopLimit (default is 1000): If a script performs a loop over 1000 iteration, the runtime will throw a ScriptRuntimeException. Set to 0 to disable loop limits.
  • RecursiveLimit (default is 100): If a script performs a recursive call over 100 depth, the runtime will throw a ScriptRuntimeException. Set to 0 to disable recursion limits.
  • StrictVariables (default is false): If set to true, any variables that were not found during variable resolution will throw a ScriptRuntimeException
  • RegexTimeOut (default is 10s): If a builtin function is using a regular expression that is taking more than 10s to complete, the runtime will throw an exception. Set to System.Text.RegularExpressions.Regex.InfiniteMatchTimeout to disable regular expression timeouts.