What is Reddit's opinion of Learn You a Haskell for Great Good!: A Beginner's Guide?
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3 reviews of this product found across Reddit:

There was a reason that I stated, "for me...". Reading balanced parens is quite easy, for me. Substituting seemingly-arbitrary glue tokens in lieu of punctuation and balanced-container tokens is very non-obvious, for me.

Note: I don't work in Haskell. I am planning to learn it (this book is on my night stand, waiting for me: https://smile.amazon.com/gp/product/1593272839/), but thus far the necessary spare time has not arrived.

Uh, I don't think there are any more (at least that I ever heard of). I do wish there a Lisp one, though. Hm, I was going to say they might have been illustrated by the same person or something; the, ah, copy right page of the one on Amazon lists "Octopod Studios" for the cover design and interior. Well that is interesting, at least (Erlang cover has an octopus).

To me Haskell seemed to come first, being more developed and available. The domain pages confirm this, showing 2008 for Learn You a Haskell and 2009 for Learn You some Erlang:
https://www.register.com/whois.rcmx

It seemed like the other was riffing or simply admiring or giving tribute.

I love this book. I almost get monads now.

And, BTW, it is going to be a book:

http://www.amazon.com/Learn-You-Haskell-Great-Good/dp/1593272839/