I'm working my way through Graham's book "On Lisp" and can't understand the following example at page 37:
If we define exclaim so that its return value incorporates a quoted list, (defun exclaim (expression) (append expression ’(oh my))) > (exclaim ’(lions and tigers and bears)) (LIONS AND TIGERS AND BEARS OH MY) > (nconc * ’(goodness)) (LIONS AND TIGERS AND BEARS OH MY GOODNESS) could alter the list within the function: > (exclaim ’(fixnums and bignums and floats)) (FIXNUMS AND BIGNUMS AND FLOATS OH MY GOODNESS) To make exclaim proof against such problems, it should be written: (defun exclaim (expression) (append expression (list ’oh ’my)))
Does anyone understand what's going on here? This is seriously screwing with my mental model of what quoting does.