I wanted to check if any of a set of keys existed in the hash, but was surprised to find that exists will only do a single key lookup. This seems like something that should be in core not just because it is syntax sugar, but because it is would be much more efficient to have the internal C code perform the multiple lookups. Example: 
my %haystack; @haystack{'aa'..'ff'} = ();
# syntax error:
say exists @haystack{qw(aa bb cc dd)};

# need to use this instead:
use List::Util qw(first);
say !! first { exists $haystack{$_} } qw(aa bb cc dd);

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In reply to Why doesn't exist work with hash slices? by Anonymous Monk

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