raku's feed operator (pipelines)

Recently, I’ve been writing a small program in Raku to help me case a sequence of words (kebab, snake, camel, etc.). This means testing a character for symbols, removing extra spaces, and various other operations. One of the functions ended up looking like this:

trim-extra-spaces(alphanumeric($s.lc)).split(" ").join("-");

I didn’t like this. Luckily for us, raku has the ==> feed operator, which seems to be similar to Elixir’s |> pipe operator. Refactored, it looks like this.

alphanumeric($s.lc)
==> trim-extra-spaces()
==> split(" ")
==> join("-")

However, I quickly ran into a problem:

sub my-func($s) {
    return alphanumeric($s.lc)
    ==> trim-extra-spaces()
    ==> split(" ")
    ==> join("-");
}

my-func("she-sells    seashells on the sea!shore").say; # "shesells    seashells on the seashore"

Adding the return was causing my tests to fail.

Although this looks like how we’d usually write a return statement, the code above won’t actually do what we’d expect! return doesn’t return the result of the operation - it just returns the result of the first function (in this case, alphanumeric). In Raku, we have naked returns, but if we really wanted to be explicit about this, we have a few options:

0. Implicit, naked return

1. Return at the end:

sub my-func($s) {
    alphanumeric($s.lc)
    ==> trim-extra-spaces()
    ==> split(" ")
    ==> join("-")
    ==> return;
}

2. Wrap the result of the operation in parentheses:

sub my-func($s) {
    return (alphanumeric($s.lc)
    ==> trim-extra-spaces()
    ==> split(" ")
    ==> join("-"));
}

3. Assign it to a variable first:

sub my-func($s) {
    my $res = alphanumeric($s.lc)
    ==> trim-extra-spaces()
    ==> split(" ")
    ==> join("-");
    return $res;
}

Personally, I’m not a fan of option 1, but that’s just me. Whatever option you do decide to go with, just be aware that returns work a little differently when you use the feed operator.