[Haskell-cafe] idea for avoiding temporaries

[John Meacham]

On Fri, Mar 09, 2007 at 10:58:43AM -0500, Jan-Willem Maessen wrote:
> * Linear or Uniqueness types are almost what we want.  I think Josef  
> Svenningson was the one who captured this the best: Uniqueness type  
> *require* that the *caller* of these routines make sure that it is  
> not sharing the data.  So we need two copies of our linear algebra  
> library---one which takes unique arrays as arguments and updates in  
> place, and one which takes non-unique arrays and allocates.  And we  
> have to pick the right one based on context.  What we want, it seems  
> to me, is one library and a compiler which can make informed judgments.

wansbrough's simple usage polymorphism paper details an analysis that
infers types that are 'polymorphic' in their usage qualities. The paper
brings up the possibility of generating specialized versions of
functions 'usage-specialization' based on these types. which seems to be
exactly the sort of thing you would want out of a compiler for the
above. 

http://citeseer.ist.psu.edu/292462.html

it would also seem like it would be possible to actually pass these
usage types at run-time and choose operations based on that.

This seems like it would be an ideal way to go, it would behave in a
very predictable way for haskell programmers used to type specialization
and haskell classes and the middle-end work wouldn't be as much as
system f is already typed and these usage types would behave like other
type variables in a lot of ways after their initial inference. usage
specialization could occur via the same RULES mechanism that type
specialization uses now...


> I'd love to hear if anyone has insights / pointers to related work on  
> any of the issues above; I'm especially keen to learn if there's work  
> I didn't know about on fusion of multiple traversals.  In my day job  
> with Fortress we are looking at RULES-like approaches, but they  
> founder quickly because the kind of problems David is trying to solve  
> are 90% of what our programmers want to do.

I think the simple usage polymorphism paper (and the thesis that goes
along with it) can provide some fertile ideas for exploration here..

        John

-- 
John Meacham - ⑆repetae.net⑆john⑈