AoC day 2 (dc)

#!/usr/bin/dc -f-

[q] SX

[
    rdd                 # 0 mag -> mag mag 0 (zero is rel-cmd, leave on top)
    lx+sx la*ly+sy r    #       -> (x += mag) mag 0 -> (y += a * mag) 0
] SF

[
    z 0 =X              # stop when stack empty

    r                   # mag cmd -> cmd mag
    102r-               #         -> rel-cmd mag (cmd now relative to ASCII 'f')

    d 0=F               # (rel-cmd = 0) rel-cmd mag

    7*13%               # sign mag (this works for -15, 0, and 2 which is all we need)
    * la+ sa            # a += sign * mag

    lLx                 # loop
] SL

0dd sx sy sa            # init x, y, a
lLx                     # start loop

[Part 1: ]n lx la* p
[Part 2: ]n lx ly* p