perl6 Hash key <$/[0]> , <"$/[0]"> and {"$/[0]"} make the values behave differently - hash

Question

I have a file in the format of type : amount and I want to put all
the lines into a hash whose keys are the types and the values are
the sum of the amounts.
However, it seems that how the types are quoted affects how the
amounts behave. Can someone explain how so?
Here is the contents of file data:
food : 100.01
gas : 50.02
food : 20.03
gas : 30.04
When the keys are constructed with %x<$/[0]> , the keys seem to be
correct, but the values seem to be pushed into an array, even though I
want to add to get the total amount:
home/lisprog$ cat data | perl6 -ne '
state %x //= {};
if $_ ~~ m/ \s* (\S+) \s* \: \s* (\d+\.\d+) \s* / {
if %x<$/[0]>:exists {
%x<$/[0]> += ($/[1].Numeric);
}
else {
%x.push: "$/[0]"=>($/[1].Numeric);
}
};
END { for %x.kv -> $m, $n { say "$m : $n"; } }' | sort
food : 100.01 20.03
gas : 50.02 30.04
The same behavior if the keys are constructed with <"$/[0]"> :
cat data | perl6 -ne '
state %x //= {};
if $_ ~~ m/ \s* (\S+) \s* \: \s* (\d+\.\d+) \s* / {
if %x<"$/[0]">:exists {
%x<"$/[0]"> += ($/[1].Numeric);
}
else {
%x.push: "$/[0]"=>($/[1].Numeric);
}
};
END { for %x.kv -> $m, $n { say "$m : $n"; } }' | sort
food : 100.01 20.03
gas : 50.02 30.04
When the keys are constructed with %x{"$/[0]"}, the keys and values
behave correctly:
home/lisprog$ cat data | perl6 -ne '
state %x //= {};
if $_ ~~ m/ \s* (\S+) \s* \: \s* (\d+\.\d+) \s* / {
if %x{"$/[0]"}:exists {
%x{"$/[0]"} += ($/[1].Numeric);
}
else {
%x.push: "$/[0]"=>($/[1].Numeric);
}
};
END { for %x.kv -> $m, $n { say "$m : $n"; } }' | sort
food : 120.04
gas : 80.06
So, how come the keys affect how values behave? Or did I ask a wrong question?

Answer 1

I think you have a misconception about what <> does. They're basically the equivalent of single quotes:
say <"foo"> # "foo"
So you're checking if a key '$/[0]' exists, which it doesn't, and then push a Pair onto the hash with the correct double quoted (although unnecessary to quote it there), which will create the correct key if it doesn't exist yet.
Since $0 is short for $/[0], m/// uses $_ by default, and non-existing keys in a hash are silently created with Any, and you can += Any just like you can in Pumpkin Perl 5, and END blocks don't need to have a block, you only really need:
$ cat data | perl6 -ne '
state %x;
%x{$0} += $1 if m/ \s* (\S+) \s* \: \s* (\d+\.\d+) \s* /;
END for %x.kv -> $m, $n { say "$m : $n" }' | sort
Actually, come to think of it, the actually smells like a Mix (https://docs.raku.org/type/Mix). Leaving that as an exercise for the reader :-)