Explode records of files into new files based on the value of a given field

explode.p6

#!/usr/bin/env perl6
%*SUB-MAIN-OPTS<named-anywhere> = True;

my %out_files;

sub MAIN( @in-files where { .IO.f // die "Input file $_ not found" },
          Int :$f(:$field) = 0,
          Str :$d(:$delimiter) = ',',
          Str :$t(:$template) = '%') {

    for @in-files -> $file {
        my $io = $file.IO;
        for $io.lines -> $line {
            my @fields = $line.split($d);
            my $file = $template.subst('%',@fields[$f]);
            $file ~= $io.extension;
            if not %out_files{$file}:exists {
                %out_files{$file} = $file.IO.open(:w);
            }
            %out_files{$file}.print($line);
        }
    }
    %out_files>>.close;

}

===SORRY!===
Shape declaration with () is reserved;
please use whitespace if you meant a subsignature for unpacking,
or use the :() form if you meant to add signature info to the function's type
at /Users/matt/bin/explode:7
------> Int :$f⏏(:$field) = 0,
Shape declaration with () is reserved;
please use whitespace if you meant a subsignature for unpacking,
or use the :() form if you meant to add signature info to the function's type
at /Users/matt/bin/explode:8
------> Str :$d⏏(:$delimiter) = ',',
Shape declaration with () is reserved;
please use whitespace if you meant a subsignature for unpacking,
or use the :() form if you meant to add signature info to the function's type
at /Users/matt/bin/explode:9
------> Str :$t⏏(:$template) = '%') {
expecting any of:
shape declaration