# Isn't that just the way of it...

I mentioned in the previous entry that I was missing Python's List
Comprehensions. Well, I've gotten a little closer to having them.
For some reason, LispMe doesn't come with a `zip` method,
and you can only get `map` by importing a "`Standard
Library`" memo. So, I had to write my own version of zip, and
here it is, for anyone else who might find it useful.

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(define (zip s1 s2) (if (or (null? s1) (null? s2)) '() (cons (list (car s1) (car s2)) (z (cdr s1) (cdr s2))))) |

Along with my halfway function, redefined to be `(define
(halfway x) (/ (+ (car x) (cadr x)) 2))`, I can now write
`(map halfway (zip current-point next-point))` to get the
point halfway between where I am, and where I am going to.

I also came to another realization. I was planning on defining a
`current-point`, and using `set!` to update it
to the new halfway point, but when I think about it, I don't really
care what the current point is at any time other than processing, so
there's no particular need to set it, and instead I should just pass
it around as a parameter, making my iter function (and I just made up
the name "iter function", based on the <a href=
"http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-10.html#%_sec_1.1.7"

sqrt-iterfunction in "Structure and Interpretation of Computer Programs") look something like this:

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(define (triangle-iter start num-iters) (if (positive? num-iters) (begin (draw-point start) (triangle-iter (map halfway (zip current-point next-point)) (- num-iters 1))))) |

Does that look appropriately Scheme-ish, do you think?