I think that in every imperative language that offers `map`, `filter`, `reduce`, or similar, the written contract of this API should state that any higher-order function handed to it as an argument must be free from side effects.
I think I’ve seen several language core APIs have this in their contract, e.g. `Stream#reduce` in Java [0] (emphasis mine):
> accumulator - an *associative, non-interfering, stateless* function for combining two values
I think I’ve seen several language core APIs have this in their contract, e.g. `Stream#reduce` in Java [0] (emphasis mine):
> accumulator - an *associative, non-interfering, stateless* function for combining two values
[0]: https://docs.oracle.com/javase/8/docs/api/java/util/stream/S...