Caterpillar

The other day, I presented how common conditional constructs can map to pattern-matching functions. But there's more to control flow! Today, let's look at iteration, starting with a simple loop in Rust:

loop {
    do_this_forever();
}

In Caterpillar, this could look like this:

{
    || do_this_forever recur
}
    eval

Here we define an anonymous function that just calls itself forever. (recur doesn't exist in the language right now. It would call the current function recursively, without having to name it. This is not possible yet for anonymous functions, but named ones could just call themselves by name instead.)

A slightly more complex loop:

let mut i = 0;
while i < 10 {
    do_the_thing();
    i += 1;
}

And the Caterpillar version:

0
{
    |10|
        # we're done

    |n|
        do_the_thing
        n 1 + recur
}
    eval

As with conditionals, I expect that Caterpillar will have more convenient constructs built on top of this, as syntax sugar. (And with Caterpillar being a functional language, I expect those to be of the map, filter, and fold variety, rather than the more imperative loops I've shown here. But the point was to demonstrate how simple loops can map to pattern-matching functions.)