Chapter One: Setup

Build Tool
We use Stack as our build tool, and HPack for package configuration. Dependencies, test modules, executables to build, compiler flags, and the like are found in packag.yaml.
Intero
 If you install Intero, you'll get a bunch of nice editor/IDE features out of the box 🚀​
Language Extensions
GHC (the main Haskell compiler) has a number of "language extensions" available. These are things that are available in GHC, but not yet in the language spec (which is updated every 10 years or so). These are primarily to modernize to the lanaguge, and make your life much easier. For reference, here's the list of extension that we have enabled standard.
ApplicativeDo, BangPatterns, BlockArguments, ConstraintKinds, DataKinds, DeriveAnyClass, DeriveFoldable, DeriveFunctor, DeriveGeneric, DeriveLift, DeriveTraversable, DerivingStrategies, FlexibleContexts, FlexibleInstances, FunctionalDependencies, GADTs, GeneralizedNewtypeDeriving, KindSignatures, LambdaCase, LiberalTypeSynonyms, MultiParamTypeClasses, MultiWayIf, NamedFieldPuns, NoImplicitPrelude, NoMonomorphismRestriction, OverloadedStrings, OverloadedLabels, OverloadedLists, RankNTypes, RecordWildCards, ScopedTypeVariables, StandaloneDeriving, TupleSections, TypeSynonymInstances, TemplateHaskell, TypeOperators, ViewPatterns
Wow, that looks like a long list! Most of these enable quality-of-life improvements with new syntax or remove boilerplate. Almost all of these are used widely in industry, and are  considered totally safe to use (and in some cases, it's masochistic to not have them enabled, like OverloadedStrings). You can read up  more on these at the extremely informative What I Wish I Knew When Learning Haskell.
We mention this here becasue you may find reference to them while on Stack Overflow, or some syntax that's not available in older references like the now woefully out-of-date Learn You a Haskell for Great Good (which I'm not even going to link).
Project Structure
A project is broken into a reusable library, executables, tests, and benchmarks.
Library
You will often see library code in a /src directory. We're following the other convention, which is to place library code in a directory shocking titled... library.
Quality
Quaity checks live in /test. We have several kinds of tests:
Type
Directory
Unit Tests
/test/testsuite
Doctests
Setup in /test/doctest; actual tests in each source file in /library
Code Linter
/test/lint
Code Coverage
/test/coverage-code
Doc Coverage
/test/coverage-docs
Benchmarks
Benchmarks live at /bench
Executables
If a project contains a single executable, it tends to live in /app or /exe. Since our project contains multiple executables, we use the name of the executable itself (for example /fission-web).
Where to Find Packages
Stackage
We use Stackage for nearly all packages. These are stable packages, grouped into "Stack resolver versions", so you don't need to worry about version numbers. Just stick them in your dependencies, and everything just works™.
package.yaml
1
dependencies:
2
  - aeson
3
  - aeson-casing
4
  - base
5
  - [...]
Copied!
Searching in Stackage can be done by name, or by type signature, which is very useful.
Hackage
You can find even more packages on Hackage. It's a very similar process as with Stackage, but to include packages
stack.yaml
1
extra-deps:
2
- alex-3.2.4
3
- ekg-wai-0.1.0.3
4
- happy-1.19.10
5
- servant-multipart-0.11.4
6
- tasty-rerun-1.1.14
Copied!
​

Syntactic Cheat Sheet

Chapter Two: Type Classes

Last modified 2yr ago

Export as PDF

Copy link

Contents

Where to Find Packages

Stackage

Hackage