I love Rich Hickey, Clojure and Haskell and I get it when he talks about functions and the unreliability of side-effecting code.

However I work in an environment where nearly all the functions I write have to read from the database, write to the database, make HTTP requests, decrement a user's balance, modify a frontend HTML component based on a click action, return different results based on the URI or the POST body. We also use PHP for the frontend, which is littered with functions like parse_str(), which modifies an object in place. All of these are side-effecting to one degree or another.

Given these constraints and the side-effecting nature of the logic I'm coding, what can I do to make my code more reliable and function-able?