Passing an environment around

[José Romildo Malaquias]

On Fri, Oct 27, 2000 at 09:07:24AM -0700, Jeffrey R. Lewis wrote:
> José Romildo Malaquias wrote:
> 
> > On Thu, Oct 19, 2000 at 09:08:16AM -0700, Conal Elliott wrote:
> > > Indeed Fran behaviors are like your alternative #1 (function passing), and
> > > hence sharing loss is a concern.  Simon PJ is right that I have a paper
> > > discussing this issue and some others.  See "Functional Implementations of
> > > Continuous Modeled Animation" on my pubs page
> > > (http://research.microsoft.com/~conal/papers).
> > >
> > > About alternative #2 (implicit arguments), would it help?  Does it eliminate
> > > the non-memoized redundant function applications, or just hide them?  For
> > > Fran, Erik Meijer suggested implicit functions to me a couple of years ago.
> > > I hadn't thought of it, and it did indeed seem to be attractive at first as
> > > a way to eliminate the need for overloading in Fran.  However, the (Time ->
> > > a) representation of Fran behaviors is not really viable, so I wouldn't
> > > merely want to hide that representation behind implicit arguments.
> >
> > It seems that implicit parameters does not eliminate redundant function
> > applications, as Conal Elliott has commented. Reading the paper
> >
> >    Implicit Parameters: Dynamic Scoping with Static Types
> >    Jefrrey Lewis, Mark Shields, Erik Meijer, John Launchbury
> >    http://www.cse.ogi.edu/~jlewis/
> >
> > (especially section 5.1) I got this impression. I would like to hear
> > from others as well, as I had some difficulties with the paper.
> 
> I am sorry you had difficulties!

The difficulties I had is basicaly due to my lack of solid knowledge on
type theory and semantic formalisms. Not that the paper was badly
written.

> Yes, as implemented using the dictionary
> translation, implicit parameterization can lead to loss of sharing, exactly in
> the same way that overloading (and HOF in general) can lead to loss of sharing.
> 
> However, I can imagine that a compiler might chose to implement implicit
> parameters more like dynamic variables in lisp.   Each implicit param essentially
> becomes a global variable, implemented as a stack of values - the top of the
> stack is the value currently in scope.  This would avoid the sharing problem
> nicely.
> 
> --Jeff

I suppose your implementation of implicit parameterization in GHC and Hugs
uses the dictionary translation, right? Would an alternative implementation
based on a stack of values be viable and even done? Does it have serious
drawbacks when compared with the dictionary translation technique?

Thanks.

Romildo
-- 
Prof. José Romildo Malaquias <romildo@iceb.ufop.br>
Departamento de Computação
Universidade Federal de Ouro Preto
Brasil