[perl #132003] grammar cannot parse from Blob/Buf

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# New Ticket Created by  Lars Dɪᴇᴄᴋᴏᴡ 迪拉斯 
# Please include the string:  [perl #132003]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=132003 >


    › perl6 -v
    This is Rakudo version 2017.07 built on MoarVM version 2017.07
    implementing Perl 6.c.

    › cat calc.pl
    use v6;
    grammar Calculator {
        token TOP { [ <add> | <sub> ] }
        rule  add { <num> '+' <num> }
        rule  sub { <num> '-' <num> }
        token num { \d+ }
    }
    say Calculator.parse('2 + 3');
    say Calculator.parse(Blob.new([50,32,43,32,51])); # '2 + 3'

    › perl6 calc.pl
    ｢2 + 3｣
     add => ｢2 + 3｣
      num => ｢2｣
      num => ｢3｣
    Cannot use a Buf as a string, but you called the Str method on it
      in block <unit> at calc.pl line 9

It appears grammars only accept strings, but I also want to parse
non-text input, e.g. binary file formats.