Date Sorting...

David Feuer
Fri, 8 Mar 2002 02:52:32 -0500

On Fri, Mar 08, 2002, Ketil Z. Malde wrote:
> I don't think it's either functional nor imperative by itself.  The
> question is how you structure it, do you say something like
>         buffer x
>         list y
>         x = readFile ...
>         y = parse x
>         quickSort y
>         print y
> (which would be imperative), or do you say something like
>         print (quickSort (parse (readFile ...)))

Unfortunately, this is wrong.  You'd have to do something more like

readFile ... >>= print . sort . parse

> which would be functional.  Note that the only really imperative part
> is the sorting, which actually changes the content of y for the
> following part of the program.  A functional implementation wouldn't
> destroy y, but create a new list with the elements from y in sorted
> order.


> I'm not sure if that made things clearer :-)
> (If you really want to implement it, look at the Prelude for some
> help, some of the things you wish to do is pretty standard fare.
> And sorting is perhaps made easier if you rearrange the list of dates
> a bit?) 

Sorting is probably easiest if you use the standard sort function.  I'm
still kind of interested in whether anyone has done work on which
purely-functional sorts are efficient, and particularly which ones are
efficient in GHC.

David Feuer