try/catch/finally

irScript try/catch/finally blocks are used to implement error handling logic. A try block may be accompanied by a single catch block, a single finally block, or both; it cannot appear by itself:

var x = 0;

try 
{ 
throw 45.5; 
} 
catch( error ) 
{ 
x = error.Value * 2; 
}

Errors caught in a catch block are implicitly typed as ScriptError, which has the following properties:

Property Name	Data type	Read only?	Description
Class	Value	Yes	Defaults to 'ScriptError'
FromScript	Boolean	Yes	true if the error originates from a irScript throw statement; otherwise false
Value	<varies>	Yes	If FromScript is true, Value returns the target of the original throw statement; if FromScript is false, Value returns the CLR exception for the error

It's important to note that irScript catch blocks can catch CLR exceptions originating outside irScript proper… for instance, DivideByZeroException or exceptions resulting from CLR interop calls). Try/catch/finally has essentially the same semantics as in the C# language; finally blocks are guaranteed to execute following their matching try block (and any matching catch block):

var x = 0; 
try 
{ 
throw 45.5; 
} 
catch( error ) 
{ 
x = error.Value * 2; 
}
finally 

{ 
x += 4; 
}

One departure from C# is that irScript allows definition of only a single catch block per try; this is primarily due to the implicitly-typed nature of irScript. Handling of multiple error types can be implemented using conditional statements inside a catch block:

var x = CallSomeFunction();

try 
{ 
if ( x.Class != "Integer" )
{ 
throw { ErrorType : "Unexpected type", Value : x }; 
}

else if( x < 0 ) 

{ 
throw { ErrorType : "Unexpected value", Value : x }; 
}

else 

{ 
// do something with positive integer value… 
} 
} 
catch( error ) 
{ 
if( error.FromScript ) 
{ 
if( error.ErrorType == "Unexpected type" ) 
{ 
x = CallSomeOtherFunction(); 
}

else 

{ 
x *= -1; 
} 
}

else 

{ 
throw error; // we decide not to handle CLR errors here… 
} 
}

Unhandled exceptions cause irScript code to halt immediately; control is transferred to the point of invocation for the irScript program.