Add List.ends_with?/2

[sabiwara]

We have several options here:

1. just call :lists.suffix (if so, perhaps we can do the same for starts_with? / prefix)
2. copy its exact implementation
3. this PR implementation - inspired by 2. but walking two lists at once and having a consistent FunctionClauseError with starts_with?/2 (see these tests)

[whatyouhide]

Why not call :lists.suffix/2 as you mentioned in 1.?

Also, this might be a silly ask, but what do you think about adding a test to stream_data for this? We have tests for Elixir stdlib in there 🙃

[josevalim]

We don't need to keep compatibility between exceptions, so delegating to :lists.suffix is fine by me. :)

[sabiwara]

Sounds good, will go with :lists.suffix 👍

Also, this might be a silly ask, but what do you think about adding a test to stream_data for this? We have tests for Elixir stdlib in there 🙃

I can! If we delegate, we'd be testing erlang's stdlib I guess, but nothing's wrong with that :)

[whatyouhide]

@sabiwara I mean we are wrapping it and we might change impl, so yeah I think still we are testing Elixir. Also, I suggested this because of the "complex" spec you wrote for the function: when I see something like that, I always thing about a property to write 😄

[whatyouhide]

Not sure if we want to inline this but looks good to me 👍

[sabiwara]

Not sure if we want to inline

Good point, that would make sense I think?

[josevalim]

We typically only inline when there is a native implementation on the other side. So this is good to go.

PS: Plus, if the type system works out, anything that is not a native implementation will have to be rewritten in pure Elixir so Elixir can prove it is correct in core.