RodgerTheGreat/JohnEarnest updated his k5 REPL to include the 'explain' option by prefixing \x - check it out! Literally step by step execution of k expressions.

http://www.reddit.com/r/apljk/comments/2y2bic/kxl_experiment...

http://johnearnest.github.io/ok/index.html

  Welcome to oK v0.1
  (inspired by K5)
    \x 1+/1+1 2 3
  1 + 1 2 3 --> 2 3 4
  1 + 2 --> 3
  3 + 3 --> 6
  6 + 4 --> 10
  1 +/ 2 3 4 --> 10
  10