BTW, some examples of AoC 19 answers in k:

ngn's; targets ngn/k (dude's a machine): https://bitbucket.org/ngn/k/src/master/aoc19/a.k

Mine; progressively porting from k7 to k9. Not as many answers and probably worse coding than ngn's, but perhaps more approachable for newcomers. https://github.com/chrispsn/aoc2019

llelf's; targets k7. Pretty slick. https://github.com/llelf/advent2019/blob/master/sol.k