ANSI Common Lisp 9 Conditions 9.1 Condition System Concepts
Common Lisp constructs are described not only in terms of their
behavior in situations during which they are intended to be used
(see the "Description" part of each operator specification), but
in all other situations (see the "Exceptional Situations" part
of each operator specification). A situation is the evaluation
of an expression in a specific context. A condition is an object
that represents a specific situation that has been detected.
Conditions are generalized instances of the class condition. A
hierarchy of condition classes is defined in Common Lisp. A
condition has slots that contain data relevant to the situation
that the condition represents. An error is a situation in which
normal program execution cannot continue correctly without some
form of intervention (either interactively by the user or under
program control). Not all errors are detected. When an error
goes undetected, the effects can be implementation-dependent,
implementation-d