Module side effects

[samhh]

This one probably can't be done, but I'm curious if anyone has any thoughts - can we lint against module side effects?

Only way I've thought of so far is to lint specifically against fp-ts and enforce that you can't call Task or IO functions in a module except within another function.

[RebeccaStevens]

I believe if you are using the rule no-expression-statement, this will prevent module side effects unless the side effect happens as a result of a function call.
If it becomes possible to ensure a function is pure in typescript then this could also be prevented.

[jonaskello]

Yes, having a pure modifier for functions in typescript would be awesome :-).

I usually try to avoid having any code outside of functions in all modules. Having side-effects happen just by importing a module is IMO never wanted. Perhaps we could check if there is anything else than function definitions in a module? That check would be less specific of course but it would eliminate any side-effect that happen on import. Or would that be too restrictive?