Do you consider implementing `Maybe#orElse()` method?

[lancedikson]

Hi, thanks for the lib. Love it! ❤️

Do you find Maybe#orElse() method useful and consider implementing it? I find it useful in order to gracefully avoid such constructions:

let maybeGTINs = getGTINsFromString(string);
if (maybeGTINs.isNone()) {
  let maybeGTINs = just(['default']);
}

with something like this:

const maybeGTINs = getGTINsFromString(string).orElse(['default']);

Monet's seem to have one, but it accepts a Maybe instance for some reason. I guess, the best implementation would be the one mentioned in this article: https://jrsinclair.com/articles/2016/marvellously-mysterious-javascript-maybe-monad/

Maybe.prototype.orElse = function(default) {
    if (this.isNothing()) {
        return Maybe.of(default);
    }

    return this;
};

[JSMonk]

Hi, thank you a lot for the words ❤️
Sounds great!
Will implement it soon.

[lancedikson]

Great! I have some spare time, so if you would like me to propose a PR, just let me know ;)

[JSMonk]

But I'm thinking about the name and semantic, because, as an example, It's presented natively in Haskell via Alternative type class. The same example in Haskell looks like:

bannerSrc = getUserBanner user <|> Just "/assets/banners/default-banner.jpg"

This mechanism is more controllable because I can make longer orElse chains like this:

bannerSrc = getUserBanner user <|> 
            getAnotherBanner <|>
            getMockBannerFor user <|>
            Just "/assets/banners/default-banner.jpg"

I'm thinking about Alternative interface implementation for Either and Maybe with or method like this:

interface Alternative<T> {
  or: (x: Alternative<T>) => Alternative<T>
}

And the example will be like:

const bannerSrc = getUserBanner(user).or(just( "/assets/banners/default-banner.jpg"));
// or
const bannerSrc = getUserBanner(user)
                         .or(getAnotherBanner())
                         .or(getMockBannerFor(user))
                         .or(just( "/assets/banners/default-banner.jpg"));

What do you think?

[lancedikson]

Yeah, looks great to me! 👍

[JSMonk]

Done in ^2.1.2 version

[lancedikson]

Wow, that was fast! Thank you!