History is proof that removing a dangerous feature can greatly improve the quality of code. Today, we have a slew of dangerous practices that compromise the robustness and maintainability of software. Nearly all modern programming languages have some form of null references, shared global state, and functions with side effects—things that are far worse than the GOTO ever was.

How can those flaws be eliminated? It turns out that the answer has been around for decades: purely functional programming languages.