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diff --git a/topics/lisp/define-condition.gmi b/topics/lisp/define-condition.gmi new file mode 100644 index 0000000..29ef4bd --- /dev/null +++ b/topics/lisp/define-condition.gmi @@ -0,0 +1,64 @@ +# Common Lisp Condition Handling + +> One of Lisp's great features is its condition system. + +> Every Common Lisp implementation has a condition system. + +> ... conditions are more general than exceptions in that a condition can +> represent any occurrence during a program's execution that may be of +> interest to code at different levels on the call stack. + +The following three quotes are from abridged from a conversation with +Ed Langley over #common-lisp:matrix.org (Thu Dec 23 07:46:30 PM EST 2021) + +=> https://github.com/fiddlerwoaroof Ed Langley's GitHub + +Why is condition handling special in common lisp compared to other languages? + +> Because code can define recovery strategies without handling the condition. + +> Any bit of code can be wrapped with restart-case to define a +> restart. This restart defines a way you could continue from any condition +> that’is signaled within the dynamic extent of the restart-case. + +> Your condition handler can do something like (find-restart ‘continue +> c) to find the CONTINUE restart associated with condition C. If the +> restart exists, it can use invoke-restart to jump to the restart which +> runs and then execution continues like normal after the restart-case form. + +* end of coversation + +# Restarts, restarts, restarts: interactive choices in the debugger + +> Restarts are the choices we get in the debugger, which always has +> the RETRY and ABORT ones. By handling restarts we can start over the +> operation as if the error didn't occur (as seen in the stack). + +``` +(divide 3 0) +;; Y can not be zero. Please change it +;; [Condition of type SIMPLE-ERROR] +;; +;; Restarts: +;; 0: [CONTINUE] Retry assertion with new value for Y. <--- new restart +;; 1: [RETRY] Retry SLIME REPL evaluation request. +;; … +``` + +# Video References + +=> https://www.youtube.com/watch?v=9K5YVbeatHs Common Lisp Study Group: Conditions and Restarts +=> https://www.youtube.com/watch?v=ErlheGSQ2kk Common Lisp Tutorial 5a: Condition System +=> https://www.youtube.com/watch?v=FsNzDC0vaks Common Lisp Tutorial 5b: Condition System Part 2 +=> https://www.youtube.com/watch?v=5xprY8GCxFQ Integrating independent condition systems +=> https://www.youtube.com/watch?v=zp0OEDcAro0 Condition Systems in an Exceptional Language +=> https://www.youtube.com/watch?v=B42IrH8cfMM Little bits of lisp - Inspecting a condition +=> https://www.youtube.com/watch?v=pkqQq2Hwt5o Immutable Conversations + +# Internet, Blog, Book, and Article References + +=> https://devpoga.org/post/2021-04-25_common_lisp_condition_system/ +=> http://www.lispworks.com/documentation/HyperSpec/Body/f_find_r.htm#find-restart find-restart +=> https://lispcookbook.github.io/cl-cookbook/error_handling.html define-condition in the cl-cookbook +=> https://www.nhplace.com/kent/Papers/Condition-Handling-2001.html Condition Handling in the Lisp Language Family +=> https://gigamonkeys.com/book/beyond-exception-handling-conditions-and-restarts.html Conditions and Restarts |