try catch

Arguments

Returns

If no error occurs, the result of evaluating the try statement. If an error occurs, the result of the catch statement.

Description

This statement catches any errors that may occur while evaluating the try statement code. If no error occurs, then try catch will finish without ever evaluating the catch statement. If an error does occur, try catch will evaluate the catch statement code immediately and the error condition will be cleared. This is usually used to protect a running program from a piece of unpredictable code, such as an event handler. If the error is not caught it will be propagated to the top-level error handler, causing the interpreter to go into an interactive debugging session.

Example

The following code:

#!/usr/cogent/bin/gamma
    
try
{
   2 + nil;
}
catch
{
   princ("Error:\n", _error_stack_, "\n");
}

Will give these results:

Error:
((trap_error #0=(+ 2 nil) (princ Error:
 _error_stack_ 
)) #0#)

The following piece of code will run an event loop and protect against an unpredictable event.

while(t)
{
     try (next_event()) catch (print_trapped_error());
}

function print_trapped_error ()
{
     princ("Error:\n", _error_stack_, "\n");
     princ("Clearing error condition and continuing.\n");
}


		

See Also

error, Statements, trap_error, protect unwind, Tutorial II Error Handling