Exception Guarantees - Exception Handling in Software - Condition Systems

Condition Systems

Common Lisp, Dylan and Smalltalk have a condition system (see Common Lisp Condition System) that encompasses the aforementioned exception handling systems. In those languages or environments the advent of a condition (a "generalisation of an error" according to Kent Pitman) implies a function call, and only late in the exception handler the decision to unwind the stack may be taken.

Conditions are a generalization of exceptions. When a condition arises, an appropriate condition handler is searched for and selected, in stack order, to handle the condition. Conditions that do not represent errors may safely go unhandled entirely; their only purpose may be to propagate hints or warnings toward the user.