In functional list manipulation, what do we call “inserting something between each item”?

Question

Occasionally I find I need to process a list by inserting a new item after each item, except the last one. Similar to how you might put a comma between each item of a list of strings.

I got fed up of coding the special case for the last (or first) item every time, so I captured the pattern in a Linq-style extension:

public static IEnumerable<T> Separate<T>(this IEnumerable<T> source, 
                                         Func<T> separator)
{
    bool first = true;
    foreach (T item in source)
    {
        if (first)
            first = false;
        else
            yield return separator();

        yield return item;
    }
}

For example, this allows me to easily programatically fill a flow document with hyperlinks, but with a line-break between each one:

para.Inlines.AddRange(_recentFiles.Select(f => f.ToHyperlink())
                                  .Separate(() => new LineBreak()));

Assuming this doesn't already exist in System.Linq.Enumerable (which is what I typically discover immediately after writing something like this), the question is, what is this Separate operation on lists usually called in other functional frameworks or languages?

Answer 1

Haskell: intersperse

Zip usually means a different operation (zip [a, b, c] [x, y, z] = [(a, x), (b, y), (c, z)])

Answer 2

It's often called Join.

Answer 3

It looks a little like string.Join(), although Join doesn't return a real list.

Answer 4

It is also called interpose in Clojure.

user> (interpose "," ["a" "b" "c"])
("a" "," "b" "," "c")

Answer 5

Sounds like doing up a zipper (British - zip), with data on the long side and the separator on the other :-)