make match safe

[davidchambers]

String.prototype.match returns null if there is no match. For example:

> 'abc'.match(/x/)
null

This change is largely copied from #13.

[paf31]

This type seems incorrect. Something like

forall r. Fn4 Regex String ([String] -> r) r r

makes more sense to me.

[davidchambers]

This is one of the lines I copied without fully understanding. I'll update the type now.

[davidchambers]

Updated. Could you explain ([String] -> r)?

[paf31]

The type r in our case is Maybe [String], so Just and Nothing have type [String] -> Maybe [String] and Maybe [String] respectively. But looking at the code, there is nothing which uses the fact that the result is of type Maybe [String], all we care about is that

• Just(m) and Nothing have the same type.
• Just takes an argument of type [String]

so we can generalize the result type from Maybe [String] to r for all r.

[davidchambers]

Terrific explanation! Thank you, @paf31.

[paf31]

Looks good, thanks. I put one comment on the code itself, though.

[garyb]

Thanks 👍

Before making a release for this I'll check that there's nothing else that needs making safe, as this should be a new v0.x.0 release given that it breaks the API yet again!