> On Nov 14, 7:35 pm, Jason Stidd <stiddsg...@gmail.com> wrote:

> > From the point of view of Haskell, the benefit of the lazy list is not
> > to shorten the list, but to only calculate what you need. The list may
> > be large (in fact you can use infinite lists with lazy evaluation),
> > but if you only evaluate or look at what you need, its faster. If I
> > have a list of 1000 items and I only need the car or the first five
> > items for instance, there's no reason to look at all 1,000 items.
> > Especially if I'm going to be looking at the list three or four times.
> > And in addition, it won't be evaluated until we absolutely need it.
> > This is a huge benefit if for some reason we don't end up needing to
> > evaluate it all.  I hope this helps.

> I'm not familiar with Haskell, but I'm sure it cannot have an infinite
> lazy list with all those items actually present. And even with non-
> lazy lists, if you only need the first 5  items, you don't have to
> look at all 1000 items either (unless you want the last 5 items -- but
> then a lazy list would not be better off).

> I think this is in line with Conrad's reply to my question, where he
> states that

> > Even though the data generated by step 1 may be prohibitively large,
> > we actually only calculate possible moves on an "as needed" basis.
> > This would only be possible by performing the calculations in step 1
> > in a lazy manner.

> But my original question remains: what is the use of MAKE-LAZY? It
> converts an *existing* list, with *all data present*, into a lazy
> list, a system which is designed to only generate the data needed.

> Note that I'm not questioning the purpose of lazy lists; I'm
> questioning the usefulness of MAKE-LAZY (other than educational).

> Cheers,
> Peter.