> Perhaps the way in is something like C++'s "const": you take a language that isn't functional and mark parts of your code as non-state-modifying, making it ea

> Perhaps the way in is something like C++'s "const": you take a language that isn't functional and mark parts of your code as non-state-modifying, making it easier to subject them to formal reasoning Or even better, you do the opposite: non-mutable is the default case, and you use special keywords when it's not.