Clojure sequence comprehensions

I am learning Clojure and I like it. Following the ThinkRelevance functional koans has given me a really good interactive playground for learning this language. Reading through examples in a book cannot compare to actually having to write code in order to solve a problem and in the process learn syntax and the rules of a language. What a concept!

I came across something in the sequence comprehensions section that I thought was interesting.

	(= [[:top :left] [:top :middle] [:top :right]
	[:middle :left] [:middle :middle] [:middle :right]
	[:bottom :left] [:bottom :middle] [:bottom :right]]
	(for [row [:top :middle :bottom] column [:left :middle :right]]
	[row column])))

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The "for" macro can loop over one (or more) groups of things and produce the vector combinations above. I was reminded while reading this of Ruby's Array#product method, which does the same thing (return the product of 2 or more arrays).

	[:top, :middle, :bottom].product [:left, :middle, :right]
	# produces
	[[:top, :left], [:top, :middle], [:top, :right],
	[:middle, :left], [:middle, :middle], [:middle, :right],
	[:bottom, :left], [:bottom, :middle], [:bottom, :right]]

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