gistfile1.pl

sub METAOP_REDUCE_LEFT(\op, :$triangle) {
    if ($triangle) {
      return sub (*@values) {
        return () unless @values.gimme(1);
        GATHER({
            my $result := @values.shift;
            take $result;
            take ($result := op.($result, @values.shift))
                while @values.gimme(1);
          }, :infinite(@values.infinite))

      }
    }

    multi sub reduce (*@values) {
        return op.() unless @values.gimme(1);
        my $result := @values.shift;
        return op.($result) unless @values.gimme(1);
        my int $i;
        while my int $c = @values.gimme(1000) {
            $i = 0;
            $result := op.($result, @values.shift)
                while ($i = $i + 1) <= $c;
        }
        $result;
    }

    # Range optimizations
    multi sub reduce ((Range $values)) {
        if (op === &infix:<+> and Int === all($values.min.WHAT, $values.max.WHAT)) {
            my $min = $values.excludes_min ?? $values.min + 1 !! $values.min;
            my $max = $values.excludes_max ?? $values.max - 1 !! $values.max;
            return (($max - $min + 1) * ($max + $min)) / 2;
        }

        return reduce($values.list);
    }

    return &reduce;
}

say [+] 100..1_000_000;