Opaque types

[blaix]

Cover the what, why, and how of opaque types. It would be nice to be able to point to this when talking about some of the upcoming changes to gren.

Maybe on the modules page, the types page, or a new page or section on common patterns.

[blaix]

I guess this is already kind of covered (without naming the concept) in https://gren-lang.org/book/syntax/modules/#exposing

but IMO unless you're already familiar with the concept, it probably doesn't make much sense on what it means or why you would or wouldn't expose a type's constructors.

[blaix]

Maybe should be added as a page to the Appendix section (that the exposing section mentioned above links to)?

or maybe a "Type Patterns" page that covers opaque, phantom, and maybe other patterns / lingo?

[robinheghan]

A "Type Patterns" page sounds like a good idea.