Exhaustiveness Checking

[erlandsona]

Curious about ex_type run on a little demo app I'm trying to put together for a talk I'm giving this Tuesday about opaque types in Elixir.
The repo is here
https://github.com/erlandsona/opaque
when I run mix type I get this output

❌  Controller.handle/1
   |
   | type error for Email._/1 with Email._(%Phone{_: bitstring()} | %Email{_: bitstring()} | %Address{city: bitstring(), state: %St{_: :washington | :tennessee | :oregon | :new_york | :colorado}, street: bitstring(), unit: nil | bitstring()})
   |
   | at ~/code/messin/lib/contact.ex:132

❌  Controller.handle/1
   |
   | type error for Address.format/1 with Address.format(%Phone{_: bitstring()} | %Email{_: bitstring()} | %Address{city: bitstring(), state: %St{_: :washington | :tennessee | :oregon | :new_york | :colorado}, street: bitstring(), unit: nil | bitstring()})
   |
   | at ~/code/messin/lib/contact.ex:131

What that's telling me is ex_type is not using pattern matching to allow the subset of a union type to pass down as just it's branch. Curious if exhaustiveness checking is implemented and if so, whether or not it supports this use case, why or why not?

[gyson]

Thanks for reporting!

It's because ex_type did not have well support with union type + pattern match for multi-clauses function case. Some basic support (include basic exhaustiveness checking) should be added via #11 . Some advanced case would be traced at #12 .

Basic support should be able to address the case (Controller.handler/1) in this issue.