Daniel Kraft <d...@domob.eu> writes: > Hi Neil, > > Neil Jerram wrote: >> Daniel Kraft <d...@domob.eu> writes: >>> I think I got the test-suite as well as a basic macro implementation >>> (the compiler framework is really cool, that was fairly easy to do); >>> recursive macros do not yet work, but otherwise it looks fine. >>> >>> However, I want to tackle quasi-quotes (besides others) now; and in >>> Elisp %nil is not only #f of Scheme but also the end-of-list marker (I >>> guess that's why simply using Scheme's #f for %nil does not work). >>> >>> I did some experiments, and it seems that Scheme respects it partially: >>> >>> scheme@(guile-user)> `(1 2 3 . ,%nil) >>> (1 2 3) >>> >>> (is %nil in Scheme a variable because it needs the unquote?) > Yes (although I'd say you need the unquote because you want to access the variable, not the other way around </nitpick>).
>> >> Do you mean why don't we just use the symbol nil? If so, the answer >> is because in Scheme, (cons 'a 'nil) should be (a . nil), not (a). > > No, I mean why '(1 2 3 . %nil) does yield (1 2 3 . %nil) while `(1 2 3 > . ,%nil) gives the expected (1 2 3). But that does not matter much > besides astonishing me, as this is only something related to the > Scheme implementation of %nil, I guess. > The *symbol* '%nil has absolutely no special status in Scheme. It just happens that Guile provides (in the default environment) a value bound as %nil that has special properties. Regards, Rotty -- Andreas Rottmann -- <http://rotty.yi.org/>
