oleg@pobox.com writes:
Jo'n Fairbairn wrote in response to Neil Mitchell:
No, that's the wrong approach because it relies on detecting something that (a) the programmer probably knows already and (b) is undecidable in general. It would be far better for the programmer to express this knowledge in the programme.
It is indeed possible -- and quite easy -- to write programs where head and tail are total functions. That issue was discussed, for example, at the end of an old message:
Oh, indeed. Come to think of it, in Ponder the list type was something like (to translate into invalid Haskell) type List t = Maybe (NonEmptyList t) type NonEmptyList t = (t, List t) but while I did some little experiments that took advantage of that, I wasn't quite avant-garde enough to leave head and tail out of the language (back then it was hard enough to get people to try functional programming at all, and leaving out the friendly-seeming functions would have made it just too strange)
P.S. Algol68 was my favorite language too.
I wrote the Ponder compiler in A68C... -- Jón Fairbairn Jon.Fairbairn@cl.cam.ac.uk http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html (updated 2006-07-14)