[darcs-users] darcs patch: Refactor add_to_list.

[Max Battcher]

Trent W. Buck wrote:
> 
> On Sat, Jan 17, 2009 at 02:29:57PM +0000, Eric Kow wrote:
> > Refactor add_to_list.
> > ---------------------
> > > +-- | Add element @x@ to list @xs@ if it isn't there yet.
> > >  add_to_list :: Eq a => a -> [a] -> [a]
> > > hunk ./src/Darcs/Repository/Prefs.lhs 382
> > > -add_to_list s [] = [s]
> > > -add_to_list s (s':ss) = if s == s' then (s:ss) else s':
> add_to_list s ss
> > > +add_to_list x xs = if x `elem` xs then xs else x : xs
> >
> > Does it matter that x is now added to the front of the list instead
> of
> > to the back?  (I guess we could do xs ++ [x] if it does indeed
> matter)
> 
> I don't know.  It passes the functional tests...
> 
> add_to_list is only used once, so I'll study the caller and try to see
> if the order matters.

As revised, it certainly appears that add_to_list is really add_to_set...
Is there an existing library call that might be better used? 

--
--Max Battcher--
http://worldmaker.net