Sometimes a break-loop is all you have. But usually there is something around it. Typically a Lisp system can run several REPLs at the same time, one might be

Sometimes a break-loop is all you have. But usually there is something around it. Typically a Lisp system can run several REPLs at the same time, one might be a break loop. You can define a function in another REPL and use it in the break-loop. You can define the function by loading code in a break-loop. An interaction might be (here in LispWorks): CL-USER 6 > (> (sin-x2 3) 0) Error: Undefined operator SIN-X2 in form (SIN-X2 3). 1 (continue) Try invoking SIN-X2 again. 2 Return some values from the form (SIN-X2 3). 3 Try invoking something other than SIN-X2 with the same arguments. 4 Set the symbol-function of SIN-X2 to another function. 5 Set the macro-function of SIN-X2 to another function. 6 (abort) Return to top loop level 0. Type :b for backtrace or :c <option number> to proceed. Type :bug-form "<subject>" for a bug report template or :? for other options. CL-USER 7 : 1 > (load "~/sin-x2.lisp") ; Loading text file /Users/foo/sin-x2.lisp #P"/Users/foo/sin-x2.lisp" CL-USER 8 : 1 > :c 1 T A function SIN-X2 does not exist. There is an error and we get a break-loop. The break-loop is one level deep. All of Lisp is available in a break-loop: the compiler, the code loader, the evaluator, ... Lisp stays with the break-loop in the context of the error. I define/write the function in a file and the load the file. Loading the makes the function available in the running Lisp. Then I use the continue restart to try to find the function again -> the error is gone