pure-lang-users

Re: [pure-lang-users] list comprehensions

[Eddie R. <er...@bm...>]

On Sun 20/07/08  3:40 PM , Jiri Spitz jir...@bl... sent:
> Eddie Rucker wrote:
> > Is there a way to create a new value from separate
> values inside a list comprehension?> 
> > ranked is a list of lists. I want to addelement 2 and 4
> and record the result if > it is positive. Yes, it is trival to do without a list
> comprehension but I want> to do it with one.
> > 
> > [v; v > 0; v = rw!2 + rw!4; rw = ranked];
> > 
> > I know this doesn't work;
> > 
> > [v; rw = ranked; v > 0] when v = rw!2 + rw!4
> end;> 
> E. g. this way:
> 
> [v; v = map (\rw -> rw!2 + rw!4) ranked; v > 0];

Thanks Jiri, that works, but it is still not in the list comprehension spirit (without filter, map, fold, and zip)
I was looking for.

If not using list comprehensions, I think a filter_map and filter_fold like the filter-map that srfi 1 offers 
would be efficient for things like this. I'll add filter_map and filter_fold to my TODO list utility library.

e.r.
 

Re: [pure-lang-users] list comprehensions

[Albert G. <Dr....@t-...>]

Eddie Rucker wrote:
>> [v; v = map (\rw -> rw!2 + rw!4) ranked; v > 0];
> 
> Thanks Jiri, that works, but it is still not in the list comprehension spirit (without filter, map, fold, and zip)
> I was looking for.

How about:

[v; v = [rw!2 + rw!4; rw = ranked]; v > 0];

(Haven't checked this, though.)

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr....@t-..., ag...@mu...
WWW:    http://www.musikinformatik.uni-mainz.de/ag

Re: [pure-lang-users] list comprehensions

[Eddie R. <er...@bm...>]

On Mon, 2008-07-21 at 05:23 +0200, Albert Graef wrote:
> Eddie Rucker wrote:
> >> [v; v = map (\rw -> rw!2 + rw!4) ranked; v > 0];
> > 
> > Thanks Jiri, that works, but it is still not in the list comprehension spirit (without filter, map, fold, and zip)
> > I was looking for.
> 
> How about:
> 
> [v; v = [rw!2 + rw!4; rw = ranked]; v > 0];
> 
> (Haven't checked this, though.)
> 
That's the ticket! Jiri's map as a list comprehension and I should have
seen that. Not making any excuses, but this sinus headache for the last
few days has got me all messed up.

e.r.