This was not parsed as a smart match, because {%hash} was taken
as a block, not a an anonymous hash.
Also, avoid to construct an anonymous hash with an odd number of
elements.
# - a regex
{foo => 1} qr/^(fo[ox])$/
-! +{0..100} qr/[13579]$/
+! +{0..99} qr/[13579]$/
# - a string
+{foo => 1, bar => 2} "foo"
%hash [qw(bar)]
! %hash [qw(a b c)]
%hash %hash
- %hash {%hash}
+ %hash +{%hash}
%hash %tied_hash
%tied_hash %tied_hash
%hash { foo => 5, bar => 10 }