Implementation of feed logic

gistfile1.txt

use nqp;

sub PROCESS-FEED($source, @stages --> Seq:D) {

    # process a stage with given code for given iterator
    my class Process does Iterator {
        has &.code;
        has $.iterator;
        has $.is-lazy;
        method pull-one() {
            nqp::if(
              nqp::eqaddr((my \pulled := $!iterator.pull-one),IterationEnd),
              IterationEnd,
              &!code(pulled)
            )
        }
        method skip-one() {
            nqp::not_i(nqp::eqaddr($!iterator.pull-one,IterationEnd))
        }
    }

    # set up the stages
    my $iterator = $source.iterator;
    my $is-lazy  = $iterator.is-lazy;
    for @stages -> &code {
        $iterator = Process.new(:&code, :$iterator, :$is-lazy);
    }

    # return the result
    Seq.new($iterator)
}

for PROCESS-FEED( ^10, ( { say "foo: $_"; 2 * $_ }, { say "bar: $_"; 3 * $_ })) {
    say "baz: $_"
}