Nullable additions

[glennsl]

Other monads like Option, Result and List has them, so I think it makes sense for Nullable to have them too.

[zth]

I like these, I think adding them makes sense. @cknitt thoughts?

[cknitt]

I like these, too, but I think the signature for map and flatMap is incorrect. It is

let map: (t<'a>, 'a => 'b) => option<'b>
let flatMap: (t<'a>, 'a => option<'b>) => option<'b>

but should be

let map: (t<'a>, 'a => 'b) => t<'b>
let flatMap: (t<'a>, 'a => t<'b>) => t<'b>

[glennsl]

Oops. Shows where I've copied them from! I'm also missing the interface file that was added a few days ago, so I need to add signatures there as well.

[cknitt]

So map and flatMap transform null to undefined. I was wondering if they shouldn't leave null being null?

[glennsl]

I kind of agree, but that requires using Obj.magic. See what you think of it in fdfb5a0

[cknitt]

Looks good to me! 👍

[zth]

Looks good to me! Looks good to you too @cknitt ?

[cknitt]

Ready to merge from my side!

BTW, would be nice to have these additions for Null, too.