Re: Easy to add with push but not to the end of a list

[Heime]

------- Original Message -------
On Tuesday, November 29th, 2022 at 8:33 AM, Marcin Borkowski <mbork@mbork.pl> 
wrote:


> On 2022-11-29, at 08:56, Heime heimeborgia@protonmail.com wrote:
> 
> > Programming has got nothing to do with engineering or craft.
> 
> 
> What is it, then? (I'm genuinely curious about your opinion.)

Programming should be included in the Department of Sports.  :)
 
> > > Singly linked lists are a tool. They are simple, lightweight,
> > > and appropriate for keeping things in sequence, and for adding
> > > things at the front. Not at the end.
> > 
> > Stefan mentioned using reverse to put it into another list. If needed
> > the execution time would not be much different than actually place
> > new elements at end of list.
> 
> 
> The difference is that you keep adding items at the front and then
> reverse the list /once/.
> 
> Another pattern you might use is to ditch lists and keep the items in
> a temporary buffer, keeping point at its end (which is easy with
> `insert'), and then traverse the buffer to gather the results as needed. You 
> might even want to keep them in a buffer as a printed representation of a 
> list, and then read it, using the Elisp parser. (I don't know what function 
> would help with that, but I'm pretty certain such a function exists.) Not 
> sure how efficient this would be, but I'd guess it could be pretty good with 
> really large number of items. Yet another option would be to keep the whole 
> list in some variable, but use another variable (say,` last') as a "pointer" 
> to the last cons of
> that list. Then, you can define `fast-append' like this: (defvar last nil) 
> (defvar my-list nil) (defun fast-append (el) "Append EL at the end of` 
> my-list' in O(1) time."
> (if (not my-list)
> (setf my-list (cons el nil)
> last my-list)
> (setf (cdr last) (cons el nil)
> last (cdr last))))
> 
> This then would be O(1).
> 
> > > Core library functions express idioms. They are expected to
> > > help people to find patterns on how to use tools appropriately
> > > (it's not much different from tools: a screwdriver has a
> > > handle, which spells "grip me here, please").
> > > 
> > > Adding a function to core (say `hsup') which suggests that
> > > it is as easy to push something at the end of a list would
> > > be misleading people to hold the screwdriver (or the knife!)
> > > at the wrong end and hurt themselves.
> > 
> > Nobody will get hurt. Just inefficient for long lists or for
> > large number of calls.
> 
> Every time someone appends to the end of a singly linked list, a cute
> kitty dies...
> 
> ;-)

Pussy Riot it is, then!
 
> --
> Marcin Borkowski
> http://mbork.pl