i just wrote a solution for adventofcode 2018 day 10 (Day 10 - Advent of Code 2018) in emacs lisp. it was really fun writing the iterations to another buffer 
in case anybody’s interested, here’s my (not particularly emacs-like) code. if anybody has any suggestions for improvement, please let me know!
;; -*- lexical-binding: t; -*-
(setq lexical-binding t)
(require 'dash)
(require 's)
(require 'f)
(defun day10--parse-line (line)
(cl-labels ((parse-pair (str)
(->> str
(s-split ",")
(-map #'string-to-number))))
(->> line
(s-split ">")
(-take 2)
(-map (lambda (p) (s-split "<" p)))
(-map #'cl-second)
(-map #'parse-pair))))
(defun day10--advance-coord (coord)
(cl-destructuring-bind ((x y) (vx vy)) coord
(list (list (+ x vx) (+ y vy)) (list vx vy))))
(defun day10--loop (coords)
(-map #'day10--advance-coord coords))
(defun day10--print (elems)
(let* ((coords (-map #'car elems))
(max-x (->> coords
(-map #'car)
(-max)))
(min-x (->> coords
(-map #'car)
(-min)))
(max-y (->> coords
(-map #'cl-second)
(-max)))
(min-y (->> coords
(-map #'cl-second)
(-min)))
(height (1+ (- max-y min-y)))
(width (1+ (- max-x min-x)))
(buf (get-buffer-create "*display*")))
(if (or (> height 100) (> width 100))
nil
(cl-labels ((get-coord (p)
(list (- (car p) min-x)
(- (cl-second p) min-y))))
(with-current-buffer buf
(erase-buffer)
(dotimes (j height)
(dotimes (i width)
(insert ","))
(insert "\n"))
(dolist (coord coords)
(cl-destructuring-bind (x y) (get-coord coord)
(goto-line (1+ y))
(move-to-column x)
(delete-char 1)
(insert "X")
)))
'done
))))
(defun day10-part1and2 (filename)
(let ((coords (->> filename
(f-read)
(s-trim)
(s-lines)
(-map #'day10--parse-line))))
(named-let my-loop ((coords coords) (i 0))
(if (not (day10--print coords))
(message "too big")
(progn
(message "loop: %d" i)
(read-char)))
(my-loop (day10--loop coords) (1+ i)))))
(day10-part1and2 "input.txt")