Mark Polesky <markpole...@yahoo.com> writes: > (define my-alist > '((a . 1) > )) > > (set! my-alist (acons 'b 2 my-alist)) > > my-alist ==> ((b . 2) (a . 1)) > > (define (alist-prepend alist key value) > (set! alist (acons key value alist))) > > (alist-prepend my-alist 'c 3) > > my-alist ==> ((b . 2) (a . 1))
There is no real copy involved; `my-alist' points to a non-immediate value and so the only reason your `set!' does not work is because it is reassigning the binding `alist' within `alist-prepend'. This smells a bit like homework, however, and so how to achieve the result you desire is left as an exercise (a very simple one at that--if it's still not obvious and this isn't homework naturally an answer will be provided, but just in case...). Ask yourself: *why* do you want to destructively modify the original list? Do you even have to modify the value of `my-alist' to achieve what you wish? -- unknownlamer: online dating is dumb in general emacsen: computer dating rocks. I love computer emacsen: I mean I really LOVE computers ;)
