In the CL condition system they have separated error detection (exception thrown) from handler selection (catching exception) and handler implementation (what are called "restarts".)
So basically instead of registering one handler (catch block) that is responsible both for determining the proper course of action and implementing it, the condition system allows you to register multiple "restarting points" which the handler can select from when deciding how to handle the error.
One of the restarts often used in debugging is restarting any of the functions in the call chain, i.e. just trying the same thing again. But just as common is varying some parameter or local variable and then restarting the function.
So basically instead of registering one handler (catch block) that is responsible both for determining the proper course of action and implementing it, the condition system allows you to register multiple "restarting points" which the handler can select from when deciding how to handle the error.
One of the restarts often used in debugging is restarting any of the functions in the call chain, i.e. just trying the same thing again. But just as common is varying some parameter or local variable and then restarting the function.