feat(exhaustive): Add support for passing a fallback function

[gvergnaud]

Solves #144 #218 and replaces #38 #219

Docs

By default, .exhaustive() will throw an error if the input value wasn't handled by any .with(...) clause. This should only happen if your types are incorrect.

It is possible to pass your own handler function as a parameter to decide what should happen if an unexpected value has been received. You can for example throw your own custom error:

match(...)
  .with(...)
  .exhaustive((unexpected: unknown) => {
    throw MyCustomError(unexpected);
  })

Or log an error and return a default value:

match<string, number>(...)
  .with(P.string, (str) => str.length)
  .exhaustive((notAString: unknown) => {
    console.log(`received an unexpected value: ${notAString}`);
    return 0;
  })

[danielsantiago]

Is there anything we can do to make this solution implemented?

[Fasaloft]

Hello @gvergnaud, I have a question: What can I do to include this awesome feature in the release? It would really help me write clean and safe pattern matching even in production.

[gvergnaud]

I think I'll include it in the next release. I'll try to ship it in the next few weeks