Yes I had that same with reduce (to be precise with foldl and foldr in Haskell). When it clicked it was such a wonderful feeling.
Reduce is very powerful stuff.
I think a couple days ago I got what a flip function means.
flip f a b = f b a
It's useful when you want to partially apply a function but the arguments are not in the place where they should be. You just flip them and that's it.
It didn't click until I saw a good example.
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