Re: Converting languages to a purely functional form

Vidar Hokstad <vidar@hokstad.name> wrote:


> Dobes Vandermeer <dobes@dobesland.com> wrote
> > Purely functional programs are, as far as I can tell, much easier to
> > operate on programmatically than regular procedural ones. Loops,
> > destructive updates, etc. make many kinds of very powerful analyses
> > rather difficult.
> >
> > This makes a pure functional language useful as a kind of intermediate
> > representation.
> |
> > To eliminate destructive updates, you'd have to change every function so
> > that it took in each global/member variable it read, and returned every
> > one that it wrote.
>
> Take a look at
http://www.inf.ethz.ch/research/dissertations/show.php?type=diss&what=11024&lang=en
>
> Marc Brandis' dissertation is focusing on creating an optimizing
> Oberon compiler that use Static Single Assignment as an intermediate
> form.


In this thesis, Marc describes a modification of SSA, dubbed GSA
(Guarded Sequential Assignment), which he considers an improvement over
plain.


The OOC project (http://sourceforge.net/projects/ooc) then used GSA to
build a working Oberon compiler, however for version 2 the maintainer
switched back to using SSA as intermediate representation. An
explanation for the switch can be found in the mailing list archive
(http://sourceforge.net/mailarchive/forum.php?thread_id=1416753&forum_id=4840),
in a nutshell (and as Vidar alluded to) GSA didn't handle multiple-exit
structures very well.

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