On Wed, Dec 01, 1999 at 08:59:09AM -0800, Jeffrey R. Lewis wrote:
> "Ch. A. Herrmann" wrote:
>
> > I had just a fast look at the following I found at the
> > page "http://www.cse.ogi.edu/PacSoft/projects/Hugs/hugsman/exts.html"
> > for dynamic scoping:
> >
> > min :: [a] -> a
> > min = least with ?cmp = (<=)
> >
> > Actually, I'm not sure how referential transparency can be established
> > with these implicit parameters. Assume min to be called at two places
> > with a different value for cmp, but with the same input list. Or is it
> > the case that the type a is bound to a particular cmp all over the program?
> >
> > Please note, that referential transparency is one main advantage Haskell
> > has in contrast to other languages .....
>
> A paper on implicit parameters will appear in POPL'00 that will answer this
> sort of question. I'll post a reference to it later when I get a chance to
> put it on my web page.
The paper can already be found on Mark Shields home page, as I have just
discovered. The URL is
http://www.cse.ogi.edu/~mbs/pub/implicit.ps.gz
>
> But in short, for `min' to be called in two places, within the same lexical
> scope, with different bindings for `?cmp' implies that there's an intervening
> `with' binding in that same lexical scope. To avoid the problem you allude
> to, we extended substitution, particularly thru `with' bindings, to preserve
> dynaming scoping (i.e. to prevent dynamic capture). Thus referential
> transparency is retained, you just have to be careful when you substitute -
> just as you have to be careful with regular static name capture.
>
> --Jeff
>
--
Prof. José Romildo Malaquias <[EMAIL PROTECTED]>
Departamento de Computação
Universidade Federal de Ouro Preto
Brasil
