/// <summary>
/// Verifies that the contents of a variable can be called as a function.
/// </summary>
/// <param name="caller">Current class context.</param>
/// <param name="variable">The variable.</param>
/// <param name="syntaxOnly">If <B>true</B>, it is only checked that has <pararef name="variable"/>
/// a valid structure to be used as a callback. if <B>false</B>, the existence of the function (or
/// method) is also verified.</param>
/// <returns><B>true</B> if <paramref name="variable"/> denotes a function, <B>false</B>
/// otherwise.</returns>
public static bool IsCallable(PhpValue variable, bool syntaxOnly = false)
{
return(PhpVariable.IsValidCallback(variable.AsCallable())); // TODO: check syntaxOnly || can be bound
}