implement explain #18
Description
example
[0 1 [dup2 +] 3 times] explain -->
[] [0 1 [dup2 +] 3 times] [0 1 [dup2 +] 3 ] [times] [0 1] [dup2 + [dup2 +] 2 times] [0 1 0 1] [+ [dup2 +] 2 times] [0 1 1] [[dup2 +] 2 times] [0 1 1 [dup2 +] 2] [times] [0 1 1] [dup2 + [dup2 +] 1 times] [0 1 1 1 1] [+ [dup2 +] 1 times] [0 1 1 2] [[dup2 +] 1 times] [0 1 1 2 [dup2 +] 1] [times] [0 1 1 2] [dup2 +] [0 1 1 2 1 2] [+] [0 1 1 2 3] []