gistfile1.txt

BEGIN my $JSON = q:to/END/;
{
    "name": "Bender",
    "input": "beer"
}
END


multi sub trait_mod:<is> (Variable $v, :$config!) {
    my $conf = from-json $JSON;
    my $name = $v.var.VAR.name.substr: 1;
    $v.var   = $conf{ $name } // die 'Unknown configuration variable';
}

my $name is config;
say $name;
my $input is config;
say $input;