Copied with permission from this reddit post.
I’m afraid you won’t get around learning some extensions if you want to become really productive in Haskell, at least if you plan to read other people’s code. From what I can tell, the community has moved a fair bit away from Haskell2010, and many extensions are considered more or less par for the course. I’ll try to give a super-brief overview over some of them; details can be found in the GHC users’ guide and on various Haskell blogs.
Record Puns and Record Wildcards make dealing with big records quite a bit more pleasant by adding syntactic sugar for pattern matching. This is never strictly necessary, but can save you a lot of typing in certain domains.
Tuple Sections add the ability for tuple constructors to be partially applied. This reduces syntactic clutter very slightly, but it’s not very hard to implement either (from what I can tell).
Multi-Way If enables more compact
ifexpressions. I haven’t personally felt the need for it, but your mileage may vary.
Empty Data Declarations is a no-brainer and simply allows you to have data types without constructors. This can be useful, for example, if you just want to have a type-level ‘tag’ that distinguishes different types from each other.
Liberal Type Synonyms, Flexible Instances and Flexible Contexts are generally harmless and basically lift a bunch of somewhat arbitrary restrictions that used to be necessary for implementation reasons (I think).
Overloaded Strings and Overloaded Lists allow you to use the builtin syntax for string and list literals for ‘string-like’ and ‘list-like’ things. For example, you can use the literal
"I am a text!"as a
Textvalue. In literal-heavy code, this can reduce syntactic clutter to a certain degree, and these extensions shouldn’t be a major portability issue.
Bang Patterns provide a bit of syntactic sugar for ‘strictifying’ data. As far as I can tell, they are a no-brainer if you find yourself writing
Typed Holes are a nice development aid that makes the compiler tell you what types it expects for code that you have yet to write. I don’t personally use them, but some people swear by them.
Scoped Type Variables are uncontroversial and very useful if you like to give functions in
letclauses type signatures.
Rank-N polymorphism is a pretty well-established type system extension which I find difficult to distil down to a quick explanation. The
STmonad prominently uses it to increase type safety.
Multi-Parameter Type Classes are very useful and many libraries (most prominently perhaps mtl) require them. Very informally speaking, where normal type classes talk about the properties of a single data type, multi-param type classes allow you to specify relations between multiple data types. The simplest example of their use is probably
convertiblepackage. Functional Dependencies are a related extension that is in many cases required to make multi-param type classes work properly.
Existential Types are a relatively old and portable extension of the type system. Their primary use case are perhaps heterogeneous collections: When you want to have a list of things that are all instances of a common type class but don’t have the same type, existentials are your friend.
Generalised Algebraic Data Types are one of the bigger extensions to the type system, but they seem to be seeing a fair amount of usage. Basically, a GADT allows constructors for a type
T ato return values with more specific types substituted for
a, such as
T String, etc. Ordinarily, all constructors would have to return values of type
Type Families are, as far as I’m aware, the most recent big addition to the type system. They are a bit of a complex beast, but enable a large amount of type-level programming, especially together with other experimental-ish extensions like Data Kinds and Type-Level Literals. At their core, type families are simply type-level functions.
Template Haskell is simultaneously controversial and being adopted quite rapidly. It enables compile-time metaprogramming (i.e. generating Haskell source code programmatically), which projects such as Yesod or Lens use to cut down syntactic clutter significantly. Be aware, though, that TH comes with a bunch of as-yet unsolved problems with regards to cross-compilation and such.
Generalised Newtype Deriving is a conceptually very straightforward extension: for a newtype defined as
newtype NT = NT X, it lets you derive all the type classes that
Xis an instance of. This can reduce boilerplate massively in certain situations, but unfortunately the extension also has a very spotty history of long-standing bugs that could be used to circumvent the type system. Roles are an attempt to tame these problems, but they come with their own set of complexities.
All in all, I’d say don’t hesitate too much on the quality-of-life syntactic stuff discussed towards the top of the list – you’ll be able to refactor it out again relatively easy anyway, should the need arise – as well as the established type system stuff (MultiParamTypeClasses, FunctionalDependencies, RankNPolymorphism, ExistentialQuantification). Do be a bit more wary of GADTs, Type Families and Template Haskell.
Empty data declarations are standard in Haskell 2010, IIRC
Pattern Guards are part of Haskell 2010 as well afaik
Don’t forget LambdaCase, which is a handy bit of syntactic sugar that went in along with MultiWayIf
My name is Steven Degutis, and I've been writing software professionally for a decade. During that time, I've written many apps and websites, quite a few technical articles, and kept up-to-date with the rapidly evolving software industry.
If you have software needs for web, mobile, or desktop, and are looking for a seasoned software professional, please reach out to me at firstname.lastname@example.org to set up a phone call.
- Self-employed – present
- Clean Coders – 5 years
- 8th Light – 2 years
- Big Nerd Ranch – 1 year
- Self-employed - 1 year
- Web: full-stack
- iOS (UIKit)
- macOS (Cocoa)
- REST APIs
- AWS / EC2 / ELB
- HTML5 / CSS
Over the past decade, I've written a total of 172 technical articles on various programming languages, frameworks, best practices, and my own projects, as I kept up-to-date and active in the software industry.
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- 2017 — "Clean code" isn't actually clean
- 2017 — Passion in your field is overrated
- 2017 — What I learned in 5 days of writing an experimental website
- 2014 — Age of the Polyglot
- 2013 — How to Program
- 2013 — Ignore the Naysayers
- 2013 — Writing Clearly
- 2012 — Reinvent the wheel
- 2010 — Good usability
- 2009 — Twitter is the wrong tool
- 2009 — We're all pretty bad at driving
- 2008 — Why I Code
|August||NDD: Narrative Driven Development|
|August||The truth about TDD|
|August||Macroframeworks vs Microframeworks|
|March||Notes on Haskell Extensions|
|February||Second thoughts on front-end tools|
|February||First thoughts on front-end tools|
|February||Some thoughts on GUIs|
|February||First thoughts on OCaml|
|February||First thoughts on Haskell|
|August||Age of the Polyglot|
|August||The history of Mjolnir|
|August||Quitting the GUI wars|
|June||Lua: my new favorite extension language|
|January||My programming life-goals|
|January||Lingua Latina, Pars I|
|January||Allocating an AST on the stack|
|April||Ruby Accessors Considered Pernicious|
|March||Reinvent the wheel|
Here are some of the projects I'm most proud of. They were created using a variety of technologies, running on several different platforms and OSes. They're all finished products, and many of them are open source.
I made Docks in 2009 for users who wanted to swap out icons in their Dock with a single click. Its unique functionality and design aesthetic attracted the attention of Apple, Engadget, MacWorld, and led to an acquisition of my start-up by Big Nerd Ranch.
This toy was made in a weekend to entertain my 1 year old daughter. It lets you create bubbles with your fingers, which then simulate physics by bumping into each other and falling.
When I couldn't find an app in the App Store that let me make very simple lists extremely quickly, I made one myself. I use it almost every day to organize and track my activities.
I created this app to increase my productivity by letting me move windows around in macOS using keyboard shortcuts. It grew into a community-driven highly extensible app, using Lua for its plugin system.
Implementing this elite social network gave me experience integrating both Apple Pay and credit card payments (via Stripe.com) seamlessly into web apps, for a frictionless and pain-free payment experience.
This isn't just any chatroom. In this web app, you can see what everyone is typing while they type it. I made this in order to scratch my itch for making real-time apps and games, and learned how to use WebSockets in the process.
This was written in 2009, before the time of Slack, when IRC was the main way for programmers to get short-term assistance from each other. Its purpose was to be a beautiful app with an emphasis on simplicity and usability over technical power.
This is an app I actually use every single day. It lets you move windows with global keyboard shortcuts. Since it uses Vim-like key bindings, it should feel pretty natural to any programmer. There's no configuration needed; it Just Works™.
As an evolution of Phoenix, Hydra was my first attempt at embedding a full Lua virtual machine into an Objective-C app, to make a lightweight and efficient window manager that focused on speed, low memory usage, low CPU usage, and overall being gentle on laptop batteries.
These may be tiny, but they're interesting technical feats.
|Lua4Swift||Swift framework for embedding Lua with a native Swift API.|
|choose||Command line fuzzy-matching tool for macOS that uses a GUI|
|music||Command line music daemon for macOS that only speaks JSON|
|hecto||Command line text editor with an embedded Lua plugin system|
|ZephSharp||Window manager for Windows using Clojure for scripting|
|management||Minimalist EC2 configuration & deployment tool in Ruby.|
|go.assert||Assertion helper package for writing tests in Go.|
|go.shattr||Go library for printing shell-attributed strings to stdout.|
|OCDSpec2||Objective-C based testing framework with Xcode integration.|