0.0.0.7 1.4.7 Exceptions.

An exception is a control construct that exits many scopes at once. Raising an exception exits active scopes repeatedly until a handler is found for the exception, and transfers control to the handler. If there is no handler, the computation terminates in some system-dependent way--for example, by entering the debugger.

There are many arguments for and against exceptions, most of which revolve around inconclusive issues of style and taste. One argument in their favor that has the weight of experience behind it is that exceptions are a good way to handle any runtime error that is usually, but not necessarily, fatal. If exceptions are not available, each procedure that might encounter a runtime error must return an additional code to the caller to identify whether an error has occurred. This can be clumsy, and has the practical drawback that even careful programmers may inadvertently omit the test for the error return code. The frequency with which returned error codes are ignored has become something of a standing joke in the Unix/C world. Raising an exception is more robust, since it stops the program unless there is an explicit handler for it.