Transformation Priority Premise Applied

[Adrock]

http://blog.8thlight.com/micah-martin/2012/11/17/transformation-priority-premise-applied.html

[Adrock]

The author walks through the iterative construction of the following Clojure code for figuring out how to make a specified amount out of coin denominations:

  (defn change-for [amount]
  (let [denominations [25 10 5 1]
        amounts (reductions #(rem %1 %2) amount denominations)
        coins (map #(int (/ %1 %2)) amounts denominations)]
    (mapcat #(take %1 (repeat %2)) coins denominations)))

He does it while trying to minimize the "cost" of the code, which is defined in an interesting way for anyone who mostly writes imperative code.