Great concrete examples, a couple of things to add about them: Handler, conditions and restarts are much more expressive than in other languages, you can signa

Great concrete examples, a couple of things to add about them: Handler, conditions and restarts are much more expressive than in other languages, you can signal a condition (the analogue of throw) with restarts attached to it which only if you desire to handle it in another part of the program where(/if) you decide to handle the conditions(the analogue to try). It is analogue to throwing an error with catch statements attached and when you write the try statemet the catch statements attach to the throw statement are made available to said catch. Kent Pitman explains it much more eloquently than me[1]. Also to add how well thought out CLOS dynamic redifining of classes is, when one redifines the change is garaunteed to happen between redefinition and the next time you access said class, as to give leeway to the implementation to decide the best strategy to do so (for example if redifining a class with 10K+ instances if you do it all at once the system may become unresponsive). Also if the redefinition isn't just adding or removing slots you can provide a function to handle the updating of slots for the redefinition.[2] [1]: http://www.nhplace.com/kent/Papers/Condition-Handling-2001.html http://www.nhplace.com/kent/Papers/Condition-Handling-2001.h... [2]: http://www.lispworks.com/documentation/HyperSpec/Body/f_upda_1.htm http://www.lispworks.com/documentation/HyperSpec/Body/f_upda...