[mercury-users] accumulator introduction

[Peter Ross]

On Fri, Jun 23, 2000 at 04:42:28PM +1000, David Overton wrote:
> On Fri, Jun 23, 2000 at 01:11:05PM +1000, Michael Day wrote:
> > 
> > Is there any way for Mercury to automatically convert this predicate to
> > use an accumulator, or is it condemned to overflow the detstack forever?
> > 
> > sum(Input, Output) :-
> >     ( if Input = 0 then
> >         Output = Input
> >     else
> >         sum(Input-1, Output0),
> >         Output = Output0 + Input
> >     ).
> > 
> > Adding an accumulator manually to make it tail recursive gives performance
> > quite close to a C loop:
> > 
> > for (i = 0; i <= Input; ++i) sum += i;
> > 
> > which is rather nice. But it would be nicer if it added the accumulator
> > itself. Is this possible?
> > 
> 
Unfortunately when I rewrote the module to support the new update state
transformation.  I removed the support for if-then-elses, I will add
that back in the next few days.

When it is back in all you need to do is add the option
'--introduce-accumulators' to your command line.

Pete
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