Comment by sheept

As the article notes, effects (at least as described in the article) are already possible in JavaScript using generators, as long as every calling function is a generator, which I assume the author finds problematic because generators are cumbersome.

I was wondering how well TypeScript can type generator-based effects. My hypothesis is that TypeScript can let you compose functions with effects, but it is not possible for it to narrow down that the result from an effect corresponds to the effect (i.e. the result of an effect will be any possible effect result used by the function).

My incomplete, untested attempt in TypeScript[0] tries to implement `enumerateFiles` and `withMyLoggingLibrary`. The type errors demonstrate TypeScript's limitation that it can't associate an effect call with its result.

[0]: https://www.typescriptlang.org/play/?#code/C4TwDgpgBAMg9gcwK...