The following code:
.sub test
$P1 = new .Hash
$P1[unicode:"\u7777"] = 'ok'
$S1 = $P1[unicode:"\u7777"]
say $S1
.end
fails to compile. (should print "ok")
$ ./parrot foo.pir
build_key: unknown type 0x10001 on unicode:"\u7777"
Note that the same code works fine if the unicode string is put into
a string register instead of used as a literal.