This repository is a tutorial. It was built to guide a talk on applicative functors and is intended to be "read" commit-by-commit. Additionally, it forms a good example of how to build, test, and release an open source Haskell package. To begin, run
> git checkout the-beginningand then continue by stepping through the repository.
This package provides an "environment parser" capable of collecting
application configuration information from the system environment nicely
while also providing static documentation. By default, Haskell includes only
the lookupEnv function
lookupEnv :: String -> IO (Maybe String)and it's not uncommon to use ad-hoc IO computations structured to build
program configuring using this primitive. However, since the environment
forms a part of the public interface of a program, it'd be nice if our
"environment parsing" were self-documenting. The end goal is to enclose most
of the practice of environment parsing in a single type, highly inspired by
Parser types like parsec or attoparsec. This type should be useful not
only for producing the program's runtime environment configuration but also
for documenting the environment configuration interface the program exposes.
For future readers following along, the Changelog file may be of use as it
summarizes the high-level changes at each commit.
git does not include a method of single-stepping through a repository
history. This is unfortunate because that's exactly the best way to explore
the material here. To fix this I've included a git command in a local
Makefile which steps to the next commit
> make step