Contributing
Adding a new transformer typeclass
First thing is the set of operations, or the signature.
For example Tell[F, E] has the signature def tell(e: E): F[Unit].
Once you've got this down, you need to come up with a set of laws and a base typeclass. These have to be worked out at the same time, because choosing base classes with more operations gives you richer potential for laws but restricts implementations severely.
Come up with a rough sketch of the laws in Scala as methods but assuming no type parameters need to be
provided and all of the operations needed are in scope; use <-> for the equality assertion.
To be continued.
Adding a new transformer typeclass instance
The characteristic which transformer typeclasses have in common is that instances of them are
commonly lifted through transformer stacks. I.e., if you have an Ask[E => ?], you can
have an Ask[EitherT[E => ?, String, ?]]; a so-called inductive instance of Ask,
because the capability is not provided by EitherT itself but the "inner monad".
Because of this, there's an argument to be made that there's only one transformer typeclass instance you should need to provide: that of the "innermost" monad, the one that is actually implementing the typeclass operations.
Running Documentation Site
The cats-mtl website runs on SBT-Microsite.
To generate the website locally, run sbt
$ sbtThis will take you to the root project.
Next, run makeMicrosite within sbt
sbt:root> makeMicrositeOnce complete, this will create a docs/target/site directory. Ensure that you have jekyll installed. In another terminal, go to the cats-mtl/docs/target/site directory, and run in your shell (not sbt):
$ jekyll serve -b /cats-mtlBrowse to http://127.0.0.1:4000/cats-mtl/ as directed by jekyll. The -b /cats-mtl is
required so that context-path is correct and all resources are resolved correctly.
Keep in mind that you can keep jekyll running while you make continuing calls to makeMicrosite in sbt.
jekyll will watch and rebuild continually as you make changes.