cppc.raku

## Returns a hash of character positions for the given string
## cp('aabb') --> {a => [0,1], b => [2,3]}
##
sub cp(Str $s --> Hash) {
    (^($s.chars)).classify({ substr($s, $_, 1) })
}

## Inverse of cp (apply join() to get the string)
##
sub pc(#`(Hash) %cp --> Array) {
    my @s;
    @s[.value.List] = (.key xx .value.elems) for %cp;
    @s
}

my $s = 'alpha';

say "'$s' --> ", $s.&cp;

say '{...} --> ', $s.&cp.&pc;

Session output

$ raku cppc.raku
'alpha' --> {a => [0 4], h => [3], l => [1], p => [2]}
{...} --> [a l p h a]

## ... uncomment 'Hash' on line 10 ...

$ raku cppc.raku
'alpha' --> {a => [0 4], h => [3], l => [1], p => [2]}
Type check failed in binding to parameter '%cp'; expected Associative[Hash] but got Hash[Any,Mu] ((my Any %{Mu} =
:a($...)
  in sub pc at cppc.raku line 10
  in block <unit> at cppc.raku line 20