how do you decide its a cmp or <=> ?

The dispatcher does that by finding the appropriate multi-sub that implements the actual comparison. 

# cmp. Generic, "smart" three-way comparator.

multi sub infix:<cmp>(Any,       Any)
multi sub infix:<cmp>(Real:D,    Real:D)
multi sub infix:<cmp>(Str:D,     Str:D)
multi sub infix:<cmp>(Version:D, Version:D)

# Compares strings with string semantics, numbers with number semantic
+s, Pair objects first by key and then by value etc.
# if $a eqv $b, then $a cmp $b always returns Order::Same. Otherwise O
+rder::Less or Order::More.

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what if you want to apply another ordering? Like Czech sorting?
Rakus Str class is fully Unicode aware and by default sorts characters on the numeric value of the codepoint. 
dd 'a ä b'.comb.sort;
(" ", " ", "a", "b", "ä").Seq;

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If you wanted to implement your own behaviour you could just add another multi 
subset CzechString of String;
multi sub infix:<cmp>(CzechString $a, CzechString $b) {
  # sort logic here
}

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Or you can simply pass your comparator to sort 
sub czech-sort(String $a, String $b) {
  # sort logic here
}

@czech-words.sort( &czech-sort );

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how do you sort by multiple criteria? Method chaining?
You can adress that in the comparator like in Perl, or make the comparator return a list of things. 
dd ([1,'z'], [2,'a'], ['1', 'a']).sort( *.[0,1] );
(["1", "a"], [1, "z"], [2, "a"]).Seq

dd ([1,'z'], [2,'a'], ['1', 'a']).sort( { $^a[0] <=> $^b[0] || $^a[1] 
+cmp $^b[1] });

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holli

You can lead your users to water, but alas, you cannot drown them.

In reply to Re^3: Spoiled by Perl (sorting sugar) by holli
in thread Spoiled by Perl by afoken

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