in reply to Abusing Map

You could do:

@b = map{ $a[ $_-1 ] + $a[ $_ ] } 1 .. $#a;

For small arrays, it doesn't cost too much.

Update: corrected bounds as pointed out by AnomalousMonk

But post-fix for is probably better:

$b[ $_-1 ] = $a[ $_-1 ] + $a[ $_ ] for 1 .. $#a;

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