The env-parser talk/repository

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-beginning

and then continue by stepping through the repository.

Description

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.

Changelog

For future readers following along, the Changelog file may be of use as it summarizes the high-level changes at each commit.

Notes on stepping through the repository

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