Re: Sort a list of dotted pairs

"Kjetil S. Matheussen" <k.s.matheussen@[EMAIL PROTECTED]
> writes:

> On Wed, 23 Jul 2008, Pascal J. Bourguignon wrote:
>
>> BastiL2001@[EMAIL PROTECTED]
 writes:
>> 
>> > Dear group,
>> >
>> > I have a list of dotted pairs that may look something like this:
>> > ((4 . something) (2 . maybe ) (3 . this ) (7 . last ) (5 . some))
>> >
>> > I want it to be sorted after the car of each dotted pair starting
with
>> > the lowest number...
>> >
>> > ((2 . maybe) (3 . this) (4 . something) (5 . some) (7 . last))
>> >
>> > Only thing I have done so far is the sort function which does not
seem
>> > to help in that case... How could this be done? Thanks.
>> 
>> It depends on how you made this sort function.
>> If you made it like Common Lisp sort, then you can just write:
>> 
>>      (sort a-list < 'key car)
>> 
>> But if you made it like the sort we usually find in scheme libraries,
>> then  you will have to write:
>> 
>
> Not really:
>
> (sort a-list function-which-compares-cars)

How many gazillons of function-which-compares-such-and-such will you
write?

With (sort a-list < 'key car) if we have 20 ways of comparing stuff
(<, string<, symbol<, etc) and 100 ways of extracting keys (100
getters), we can sort 2000 different way.


With (sort a-list function-which-compares-cars) you would have to
write 2000 function-which-compares-some-key-some-way before.


-- 
__Pascal Bourguignon__