hmmm. It seems that mzscheme (at least the version that I'm running arc on, 360) doesn't support optional args. I guess I'll have to do it some other way.
It's fairly tedious to be doing this in Scheme, isn't it? We might let Scheme handle implementing the low level readc, and then in Arc redefine readc to be a more advanced function that can take an optional argument:
(mac redef (name parms . body)
" Redefine a function. The old function definition may be used within
`body' as the name `old'. "
`(do (tostring
(let old (varif ,name nilfn)
(= ,name (fn ,parms ,@body))))
,name))
It's the same as yours, except (a) it suppresses the warning on re-assigning an identifier, and (b) it calls the original function old.
btw, why is there no peekb? Or any other functions that work on bytes?
As part of the design process of finding the shortest Arc implementation, pg is careful not to include functions that he isn't actually using for news. This leads to some surprises (car, cdr, cadr, cddr, but no cdar?) but also removes cruft that builds up implementing things that people might need some day but turn out not to.
It turns out not to be a problem, since Arc is so concise it's really easy to extend, and so people quickly implement the things they need that pg happens not to be using for news.
I find I prefer the Arc approach, since libraries that try to provide everything I might need often have so much stuff that ironically they make it harder to implement what I actually need.
If you need the change right away you can patch ac.scm yourself, or, if you don't mind waiting, pg will eventually have a new arc3.tar containing the update.
