Nice solution, more readable, IMHO. One question though, - what did you mean under
The second (
acc) contains the individual steps of the final handshake.
A simple example would be great.
Thank you 
belgoros
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NobbZ
With that I mean that the accumulator accumulates the list of handshakes that have to be returned and found so far.
My submission from 7 years ago is still public, and even though I updated it today to pass the tests (a simple rename of files), I can not figure how to publish the latest version…
As you can see, the individual handshakes from the 3rd argument get incrementally added to the front of the acc in the recursive calls. So this list is build up in reverse. Therefore, if the secret code demands a “reversal” of the handshakes, I return the accumulator as is, and if no “reversal” is demanded, I reverse it, to get it forward.
This building in reverse is common when recursively buiding a list.
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belgoros
Yep, seeing it all together clarifies the solution. Thank you!
As for re-submitting a new version, you can always do it by running
exercism submit lib/secret_handshake.ex from your terminal (excersism CLI should be installed first).
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