fp-intro-effects
This is a small repo of the code to be used in my workshop: You are closer to FP than you may think.
The repo is not self-explanatory, but everything should make sense after attending my workshop.
Goal
The goal is to refactor an existing imperative program that has side effects (in this case, an innocent implementation of persistence using a file) into 3 programs:
- The same imperative program
- A total program that encapsulates errors into the return type (instead of throwing exceptions)
- A side effect free program that returns programs that will eventually run side effects when run at the end of the world (except that one won't handle exceptions for simplicity)
Usage hints
This repo is designed to be used with groll to guide you through a step by step refactoring. To use it:
- Install groll globally, by adding
addSbtPlugin("de.heikoseeberger" % "sbt-groll" % "6.1.0")to your~/.sbt/1.0/plugins/plugins.sbt(create the file if missing) - Clone the repository
- Launch sbt
- At the sbt command prompt, run
groll initial - Read the code, think about next step
- At the sbt command prompt, run
groll next - Iterate from 5
If you want to see how the Async version of the program is implemented step by step you can manually checkout the
commits in the async branch by hand. Otherwise you'll se all of them in a merge commit when you groll next after the
Result implementation.
Disclaimer
The abstractions implemented here have the sole purpose of teaching functional programming. In particular, some aspects that I considered out of the scope of this workshop should NOT be left out of any professional implementation:
- Typeclasses should have laws, so that you can reason about what they abstract over
- The implementations of
ResultandAsyncshould be stack safe, so that you don't blow the stack when you run a long chain offlatMaps. - The implementations given here don't care at all about performance. Having an unperformant Monad like this can lead to performance problems in real programs.