There has been a long-standing issue within Arcueid: dealing with nested quasiquotes. Apparently reference Arc doesn’t handle this case all too well either, and as such none of the code that I use for compatibility testing like news.arc and others makes use of nested quasiquotes either. However, it seems that macro expansions in general might well result in cases where nested quasiquotes can arise, so it is important that this issue be fixed. Anyhow, in my searches I ran across a link to an implementation of a Common Lisp-style quasiquote as Arc macros. It’s an interesting exercise converting it to C… I suppose you might say that this is an example of a macro in Arcueid’s C code, however, it isn’t precisely implemented that way, but as a hook in the compiler, as this is a fundamental part of Arc’s functionality.
The basic example of a nested quasiquote is the following:
``(+ 1 ,,@(list 2 3) 4)
Current Arc 3.1 and Anarki both produce
(+ 1 2 4) when asked to evaluate that. Common Lisp produces
(+ 1 2 3 4), which is, I think, what we should be doing. Scheme (Racket) produces an error when presented with the same. Arcueid 0.1.1 and below produce a similar error. Akkartik mentions that this was working in some previous version of reference Arc, though he can’t seem to remember when. I think we should produce the same results as Common Lisp for nested quasiquotes.