A functional splice, though, shouldn't have side-effects.
Then use a slice instead. No, that's not Perl keyword, instead, it's a pattern you implement using array indexes.

Since we need the same random index more than once, I stuff it into a temporary variable. I don't think you consider those very "functional", but what the heck... 

sub quite_functional_FY {
    my $i = int rand @_;
    return @_ ? ($_[$i], quite_functional_FY(@_[0 .. $i-1, $i+1 .. $#_
+])) : ();
}

[download]

I think you can get a faster implementation by avoiding the recursion for lists that don't need shuffling: lists of one item (or less: 0). 

sub quite_functional_FY {
    my $i = int rand @_;
    return @_ > 1 ? ($_[$i], quite_functional_FY(@_[0 .. $i-1, $i+1 ..
+ $#_])) : @_;
}

[download]

In reply to Re^3: Functional shuffle by bart
in thread Functional shuffle by Roy Johnson

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