On: Gamedev in Lisp. Part 2: Dungeons and Interfaces

[_19qg]

LOOP has the DO functionality included.

Example:

    CL-USER 18 > (do ((a 1 (+ a 1))
                      (b 10 (* b 1.5))
                      (c nil))

                     ((> a 5) (list a b (reverse c)))

                   (push (* a b) c))

    (6 75.9375 (10 30.0 67.5 135.0 253.125))

    CL-USER 19 > (loop for a = 1 then (+ a 1)
                       and b = 10 then (* b 1.5)
                       and c = NIL then c

                       when (> a 5) do (return (list a b (reverse c)))

                       do (push (* a b) c))

    (6 75.9375 (10 30.0 67.5 135.0 253.125))

[medo-bear → _19qg]

You can also express LOOP constructs in terms of DO. However if you were to construct a more exotic iterator that is not so straight forward in LOOP (beware of edge cases), I think it is more reasonable to pick DO. I think also that your example illustrates this.

[_19qg → medo-bear]

I would miss the in-order collects, actually collect/maximize/... features, destructuring of lists, direct type declarations, ...

I also find DO not easy to read and understand.

The code from above I would actually write in LOOP as

    (loop for a from 1 upto 5
          and b = 10 then (* b 1.5)
          collect (* a b) into c
          finally (return (list a b c)))

I find that to be readable.

[medo-bear → _19qg]

Of course to each their own. I like LOOP a lot actually when I need to do something familiar, however for something unfamiliar DO is often my choice. It also serves as a caution to tread and think carefully when I return to the code. Sometimes, after a while, I realise how to do the DO construct succintly with LOOP