From @gfldex

m​: my %h{<a b c>};
# OUTPUT«===SORRY!=== Error while compiling /tmp/FOE9PcfY9f␤Invalid hash
shape; type expected␤at
/tmp/FOE9PcfY9f​:1␤------>my %h{<a b c>}⏏;␤ expecting anof constraint␤»

# expected output NYI

m​: my %h{'a', 'b', 'c'}; %h<e> = 666; %h.gist.say;
# OUTPUT«e => 666␤»
# expected output NYI or wrong keylist as this form is not specced