> The question becomes, though, why are A and B suddenly interlinked? Why was this context not already in place? Here's an example, roughly taken from a projec

> The question becomes, though, why are A and B suddenly interlinked? Why was this context not already in place? Here's an example, roughly taken from a project I did not too long ago (in an imperative language, not a functional language). Suppose you have an e-commerce system. One day, the business decides to start giving out coupons, say for 10% off. Any order can have a 10% off coupon applied to it. All is fine and good, orders now have an optional coupon attribute, you compute order totals in an obvious way, coupons are nicely orthogonal to the rest of the system. Then some time later, we decide to add free shipping coupons. But, there's a wrinkle: they only apply to ground shipping. Now, you can only add a free shipping coupon to an order with ground shipping; and, also, if the user changes their shipping method, you have to go look to see if they have a discount which now must be removed from the order. Now, two previously independent aspects of order placement and processing are coupled together. Because this was written in an imperative language and backed with a stateful database store, it was mostly trivial to make the changes required. This scenario is not actually as bad as the situation the OP described, but my feeling is that it would be more difficult to have dealt with in a pure functional environment. (BTW, this is actually a fairly mild example of the sort of complicated, non-orthogonal rules which come up in e-commerce systems. I picked it not because it was the hardest to translate to a functional paradigm, but because it was easy to explain in a couple paragraphs.)