Added Lisp implementation for bubble sort

[Trashtalk217]

Added my name twice to CONTRIBUTORS.md but I have no clue how to fix it.

[PudottaPommin]

I think it should be possible to modify this file on Github and remove that duplicate line

[berquist]

Based on my understanding of idiomatic Lisp, I think this is fine, algorithm-wise.

Stylistically, indentation should be 2 spaces, not 4.

You also forgot to add the implementation to the book. I'll make a PR on your branch.

[berquist]

I would make this an actual comparison:

(print (sort (list 5 4 3 2 1) #'<)))

-;;Use of an array insead of a list would be faster
-;;The built-in sort is also quicker (sort (list 5 4 3 2 1))
-(print (bubble_sort (list 5 4 3 2 1)))
\ No newline at end of file
+;; Use of an array insead of a list would be faster
+(print (bubble-sort (list 5 4 3 2 1)))
+;; The built-in sort is also quicker:
+(print (sort (list 5 4 3 2 1) #'<))

[PudottaPommin]

Is insead correct word?

[Trashtalk217]

@MichalHanajik I type really fast ok ;)

[berquist]

Replace this with a line on how to run it:

;;; Run as `clisp bubble_sort.lisp`

[berquist]

bubble_sort -> bubble-sort to be idiomatic.

[jiegillet]

Get rid of the comparison, the other comments are there more for discussion.

[jiegillet]

This comparison part below is not useful, you can get rid of it

EDIT: Sorry, I just saw that this was suggested for you to add. Still get rid of it though ^^

[jiegillet]

Why don't you use an array then?

[Trashtalk217]

A list looks a bit prettier and - turns out - an array doesn't work with nth, which only works with lists. I probably need to look at that code or that comment... :(

[jiegillet]

Simply remove the comment and don't open the can of worms :)

[jiegillet]

For the moment you're using nth and swap to check and swap the values, which are both O(n). It's not like we are aiming for performance here, but it seems like you could do make everything a little tighter by navigating through the list and making changes as they come up, and loop over that process only once. I don't know Lisp, so I don't know if it's hard to do, though.

[Trashtalk217]

I'm sorry, but I don't think I can fix this. Other sorts are way easier to implement, and my knowledge of lisp is limited. I could just copy it from elsewhere and it would be more efficient. But should I do that?

[jiegillet]

No, no, don't copy code. And I know how awkward bubble sort is for functional programming, I did it in Haskell.
I was thinking go a function like this (in pseudocode):

function bubble-up (list):
  if length(list) < 2 : return list
  else:
    if first(list)>second(list): second(list) + bubble-up (first(list) + rest of the list)
    else: first(list) + bubble-up (second(list) + rest of the list)

Then you run bubble-up n times and voila. Is that difficult to implement?

[jiegillet]

I think (cons (second list) (rest (rest list)) ) is the same as (rest list)

[Trashtalk217]

Good point!

[jiegillet]

Looks good, thanks a lot!