I had the opposite experience with learning J. After a couple of days meditating about concept of rank (here is the most relevant part of the excellent book - <a href="http:&#x2F;&#x2F;www.jsoftware.com&#x2F;help&#x2F;jforc&#x2F;declarations.htm#_Toc191734321" rel="nofollow">http:&#x2F;&#x2F;www.jsoftware.com&#x2F;help&#x2F;jforc&#x2F;declarations.htm#_Toc191...</a>) it went much easier. On the other hand, with Haskell I can even write monads myself now, but I hardly see their usefulness yet.