# Common Lisp

    (setq *debugger-hook* (lambda (a b) (abort)))

    (defparameter *old-paren* (get-macro-character #\())
    (set-macro-character #\( (lambda (stream char)
                               (funcall *old-paren* stream char)
                               (values)))

Step one is to disable the debugger. I do this by binding the `*debugger-hook*` (which is called immediately before entering the debugger) to a function which cancels whatever tried to enter the debugger in the first place. Then, I turned `(` into a comment character- everything up to its matching close paren is completely ignored. I cache the existing function used to parse lists in `*old-paren*` so I don't have to reimplement the logic for parsing lists just to comment them out.


The result, tested on sbcl at the repl (both line-by-line and `#'load` ing it from a file), is a repl which completely ignores any meaningful code. Literal values (number, strings, symbols, etc.) work just fine, but anything else is just ignored.