----- Original Message -----
From: "Damian Conway" <[EMAIL PROTECTED]>
To: "Perl 6 Language" <[EMAIL PROTECTED]>
Sent: Thursday, February 19, 2004 8:29 PM
Subject: [perl] The Sort Problem: a definitive ruling
> C<sort> in Perl6 is a global multisub:
>
> multi sub *sort(Criterion @by: [EMAIL PROTECTED]) {...}
> multi sub *sort(Criterion $by: [EMAIL PROTECTED]) {...}
> multi sub *sort( : [EMAIL PROTECTED]) {...}
>
> where:
>
> type KeyExtractor ::= Code(Any) returns Any;
>
> type Comparator ::= Code(Any, Any) returns Int;
>
> type Criterion ::= KeyExtractor
> | Comparator
> | Pair(KeyExtractor, Comparator)
> ;
snip
> If a key-extractor block returns number, then C<< <=> >> is used to
compare
> those keys. Otherwise C<cmp> is used. In either case, the keys extracted
by
> the block are cached within the call to C<sort>, to optimize subsequent
> comparisons against the same element. That is, a key-extractor block is
only
> ever called once for each element being sorted.
>
>
How do you decide whether a key-extractor block returns number? Do you
look at the signature, or do you simply evaluate the result of the
key-extractor for each element in the unsorted list? For example, what is
the result of the following code?
sort {$_.key} (1=> 'a', 10 => 'b', 2 =>'c');
There is nothing in the signature of the key-extractor to suggest that
all the keys are numbers, but as it turns out they all are. Will the sort
end up being numerical or alphabetic?
Joe Gottman
