As you already know, apart from simple expression evaluation, the ExpressionEvaluator allows you to evaluate small scripts which contain methods and variables, etc. Scripts are nothing but just a series of expressions separated by ; character and led by several additionals keywords.
Currently, the following keywords are supported to use inside a script.
| Type | Keyword | Description |
|---|---|---|
| Conditional | if |
Identifies which statement to run based on the value of a Boolean expression. |
| Conditional | else if |
Identifies which statement to run based on the value of a Boolean expression. |
| Conditional | else |
Identifies which statement to run based on the value of a Boolean expression. |
| Loop | do |
Executes a statement or a block of statements while a specified Boolean expression evaluates to true. |
| Loop | for |
Executes a statement or a block of statements while a specified Boolean expression evaluates to true. |
| Loop | foreach |
Executes a statement or a block of statements for each element in an instance of the type that implements the IEnumerable interface. |
| Loop | while |
Executes a statement or a block of statements while a specified Boolean expression evaluates to true. |
| Jump | break |
Terminates the closest enclosing loop or switch statement in which it appears. |
| Jump | continue |
Passes control to the next iteration of the enclosing while, do, for, or foreach statement in which it appears. |
| Jump | return |
Terminates execution of the method in which it appears and returns control to the calling method. |
| Exception | throw |
Signals the occurrence of an exception during program execution. |
| Exception | try-catch |
The try-catch statement consists of a try block followed by one or more catch clauses, which specify handlers for different exceptions. |
| Exception | try-finally |
The statements of a finally block run when control leaves a try statement. |
| Exception | try-catch-finally |
A common usage of catch and finally together is to obtain and use resources in a try block, deal with exceptional circumstances in a catch block, and release the resources in the finally block. |
The following example evaluates the script, which contains multiple if and elseif statements.
class MyClass
{
public int Marks { get; set; }
public string Grade { get; set; }
}
public static void Example1()
{
string script = @"
if ( a.Marks >= 80)
{
a.Grade = 'A';
}
else if (a.Marks >= 70)
{
a.Grade = 'B';
}
else if(a.Marks >= 60)
{
a.Grade = 'C';
}
else if(a.Marks >= 50)
{
a.Grade = 'D';
}
else
{
a.Grade = 'F';
}
";
var myClass = new MyClass() { Marks = 79 };
var register = new TypeRegistry();
register.RegisterSymbol("a", myClass);
var expression = new CompiledExpression(script)
{
TypeRegistry = register,
ExpressionType = CompiledExpressionType.StatementList
};
expression.Eval();
Console.WriteLine("Grade: {0}", myClass.Grade);
}
Now let's consider another example of a script that contains a for loop.
class ClassA
{
public int i { get; set; }
public int sum { get; set; }
}
public static void Example2()
{
string script = @"
for(a.i = 0; a.i < 10; a.i++)
{
a.sum += a.i;
}";
var myClass = new ClassA();
var register = new TypeRegistry();
register.RegisterSymbol("a", myClass);
var expression = new CompiledExpression(script)
{
TypeRegistry = register,
ExpressionType = CompiledExpressionType.StatementList
};
expression.Eval();
Console.WriteLine("Sum: {0}", myClass.sum);
}