C9 Lectures: Dr. Erik Meijer - Functional Programming Fundamentals Chapter 6 of 13

I think it's truly great that you do these, I know Don has already spoken several places about F# but a concentrated lecture series is really something which will be even more beneficial to it.

Allright, back to the lazy world

I couldn't resist the Zip homework first, it looks extremely simple, first with tuple-zip

public static IEnumerable<Tuple<A, B>> Zip<A, B>(this IEnumerable<A> ps, IEnumerable<B> qs)
{
    var pe = ps.GetEnumerator();
    var qe = qs.GetEnumerator();
    while (pe.MoveNext() && qe.MoveNext())
        yield return new Tuple<A, B>(pe.Current, qe.Current);
}

Then we can verify that this behavior is correct by matching up with the built-in behavior

var ps = new[] { 1, 2, 3 };
var qs = new[] { 1, 2, 3, 4, 5, 6 };
var z1 = ps.Zip(qs, Tuple.Create);
var z2 = ps.Zip(qs);
foreach (var x in z1)
{
    Console.Write(x);
    Console.Write(", ");
}
Console.WriteLine();
foreach (var x in z2)
{
    Console.Write(x);
    Console.Write(", ");
}
Console.WriteLine();
Console.Read();

It's trivial to rewrite the tuple definition to the generic function definition.

Took a look at Bart's Zip blog post, it also mentions exceptions. How about an expression tree transformation that takes an exception-throwing iterator and rewrites it to force the exceptions first, defining a second helper iterator for the rest. Don't know if it's possible.

A less ambitious (and alas less desirable) approach is to implement a first-is-strict combinator that forces and memoizes the first element of the iterator, if there is one, thus forcing the initial exception into the light.

Nontheless, both of these approaches are inferior: they delay the inevitable: that some nested throws clause will pop up in the middle of an iterator. This sucks for exceptions as "control flow" rather than proper return types you can examine using regular if statements rather than try/catch.

(Not appropos: see this video (from LtU post): - is the world of tomorrow a flashback to the past? Beautiful unicode in APL - when will this come to mainstream; waiting since the sixties seems cruel and inhuman to me! The video also contains a mention of funny puns on the APL name, like APL π, pronounced "apple pie"; and a quote: "changes of a fundamental kind take a long time" - I'll buy that for a dollar)