For learning the concepts, something that I found rather enlightening was writing map/filter/every (and I guess, some or any, and really just about any function

For learning the concepts, something that I found rather enlightening was writing map/filter/every (and I guess, some or any, and really just about any function that operates on a collection), -with- a reduce. Then, write your own recursive implementation of reduce. I found it really helpful in grokking what these things did, and more broadly improved my understanding and use of functional composition