Alexandr Kurilin from

Front Row Education

recently wrote an article about their usage of Haskell for the Commercial Haskell Special Interest Group. I asked his permission to post that article to our blog as well.

The mission

Front Row Education was founded to change the way math education

is done in a modern day classroom. In the web universe we have all

sorts of great tools for tracking, analyzing and incentivising user

behavior: complex analytics, rich data visualizations, a/b testing,

studying usage patterns over time, cohort analysis, gamification

etc. We figured: instead of using the above to have granny click on

more ads, let's make these powerful techniques available to

teachers, parents and school administrators to make math education

more engaging and effective.

Front Row allows schools to track student progress over time,

identify areas of struggle, learn how to address them, all the

while encouraging more quality practice. Learning math this way

becomes a interactive and compelling experience, providing

immediate feedback and adjusting content with every answer. As

students practice, they generate rich data that school staff uses

to continuously course-correct and fill in the gaps.

Numerous experiments from past years show that making Front Row

a regular part of a math classroom leads to improved conceptual

understanding, a lower rate of students falling behind, and

improved scores on state tests. As of today Front Row helps over a

million students in their regular math practice, and has been used

in over 30% of US K-8 schools.

Our journey to Haskell

As of today Front Row uses Haskell for anything that needs to

run on a server machine that is more complex than a 20 line ruby

script. This includes most web services, cron-driven mailers,

command-line support tools, applications for processing and

validating content created by our teachers and more. We've been

using Haskell actively in production since 2014.

At the time of the switch we were already familiar with the

functional programming world. The central piece to the Front Row

system is the JSON API used by both the student and teacher web

experiences. I wrote the first version of the API in 2013 in

Clojure on top of the Ring/Compojure micro-framework. At the time I

didn't have plans for the API to grow to serve the kind of size and

traffic we see today: it was mostly a way for me to really dive

into functional programming and understanding design challenges

that other popular frameworks had to come across.

Building your own framework is a fantastic learning experience,

but it is also a significant commitment: without investing a ton of

time and effort into the framework, you'll end up with something

very bare-bones and hard to turn it into a production quality,

fully-featured application. It takes innumerable iterations to make

a framework extensible, modular and well maintained with a team of

1-3 developers, busy with dozens other tasks that a fast-moving

startup demands.

Clojure at the time didn't offer any alternatives as far as web

frameworks were concerned, and we were already starting to see the

inherent critical weakness behind building large modular systems in

dynamically typed languages: refactoring is a serious pain and

something you will avoid at all costs because it's hard to ensure

you're not breaking anything. It's not that bad if you have ONE

codebase that doesn't have dependencies, but once you get into two

digits you're in for a bad time.

Switching to Haskell and the Yesod framework seemed like a

natural step forward: a strongly typed, purely functional, highly

expressive language that would finally allow refactoring and moving

fast to be painless. On top of it, a beautifully designed,

extensible web framework with years of polish, one of the best

high-performance web servers in the industry, extreme attention to

type safety, and an all-star team of OSS contributors supporting

it.

Moving from Clojure to Haskell didn't feel like a massive jump:

a lot of concepts translate pretty closely, although Haskell offers

a much richer vocabulary than just maps and vecs. Monads, type

classes, IO etc. eventually clicked, and it was smooth sailing

after that.

Advantages of using Haskell

Where does Haskell fit into all of this you say? As the

development team of a small early stage edtech startup, we have two

main goals:

1. Iterate as fast as possible on new educational concepts,

   business model experiments and user feedback. Basically, crank out

   as much code as possible while keeping the quality bar very

   high.

2. Stretch our runway, be conservative with our very limited resources

Haskell fits in pretty well with both of goals.

Static typing

First of all, static typing is essential when it comes to

keeping the system always in a working state. Coming from a

dynamically typed universe, it's surprising how much time you can

save on writing unit tests, because you are getting more certainty

from the compiler: no more null exceptions, no type mismatches in

function calls, no more forgetting about dealing with the empty

list case etc. A whole class of pesky, incredibly common and banal

bugs is eliminated from your work: you now have more bandwidth to

worry about implementing user stories instead of obsessing that

your application doesn't blow up due to sloppy oversight.

I still remember one of my biggest Haskell/Yesod "aha" moments:

not only does Yesod make sure that routes in your HTML are

type-safe, but even image files linked in tags are verified to

exist on disk by the compiler. No .jpg, no build, it's that simple.

It's a level of guarantee that dramatically increases your

confidence in the code at barely any cost.

Modularity

Modularity is another big one. We have a central module at the

bottom of every one of our web applications, APIs, tools and cron

binaries. This module wraps the database entities and the SQL logic

necessary to access them. It also provides a lot of common shared

functionality that should not be implemented more than once. Since

the schema changes very aggressively, we need a way to make sure

our applications are updated ASAP, we can't wait for things to blow

up in production. Updating our entity definitions in that one

module prevents every application built on top of it from compiling

again until the change is dealt with.

No more API call mismatches, no more using an old schema, no

more apps running against an old deprecated version that can lead

to breaking the db state. As many others have stated, Haskell is

the first language out there that feels like it manages to achieve

true modularity: purity and defining what context a function is

allowed to run in ensure that a library call can lead to no

surprises. Testing side-effect free functions is much simpler than

continuously dealing with system state.

Efficiency

Regarding the second point, why would Haskell stretch your

runway? Simple. You're writing fewer bugs, you're reusing more

code, new developers are causing less damage, and you have more

room to deal with technical debt before it bites you. Purity and

static types allow a team to aggressively refactor the codebase

without having to worry that they might have forgotten to update

something: a combination of a light layer of spec-style tests and a

very picky compiler provide you with most of what you need to make

refactoring a non-issue. More refactoring = more long-term

productivity, higher team morale, more pride in one's work. Doing

the same with a Ruby is as fun as pulling teeth.

All of the above adds up to needing fewer developers, as less

time is spent on maintenance, which ultimately equals a higher

chance of your company getting somewhere thanks to the more

frequent iterations. The more stuff you try, the more likely you

are to find or expand that business mechanic that will carry your

business forward.

Trouble in paradise

This is not to say that things aren't all perfect though, and there's still plenty of room for improvement in the ecosystem.

Building

Build times, especially once the whole constellation of Yesod

and Persistent packages are brought into the mix, are not

insignificant. It still takes a good 5-10 min to build our larger web application on our beefiest machines. There are optimizations that can be made in this space which we haven't adopted yet, such as caching already build object files to avoid having to re-compile them every time, so I'm confident this will be a non-issue in the nearby future, but it's still worth being aware of. GHC works hard, you need to provide it with enough juice or time to let it do its job.

Testing

The testing frameworks out there are still fairly spartan from

the developer experience standpoint. If you test Yesod with hspec,

the premier BDD library for Haskell, there's currently no way to

insert a bunch of rows into the database during fixtures and pass

the results into the individual test cases. You have to wrap each

test case in additional function calls to pull that off, adding

more boilerplate to your tests.

Additionally, it's not possible to find out which one of your

specific test cases failed when checking for multiple conditions

within the same "it" block. This means that if you need to check

the state of the system after an HTTP request, you have no clue

which one of the checks failed.

Fortunately the developer(s) behind these libraries are

responsive and happy to look into improvements. At the very least

they're glad to point other developers in the right direction

towards a PR.

This has in general been my experience with the Haskell

community: things aren't perfect, but folks are always looking for

a way to improve the ecosystem and want Haskell to be the best

language to develop in. People are trying to carve out their little

slice of paradise, and are willing to put in the hard work to make

it happen.

Docs

Documentation is still not quite there and the initial

onboarding of new developers is still rough. There are only so many

snippets to Google for, compared to e.g. Ruby and Python. A lot of

documentation is very barebones and requires diving straight into

the source, which is fine for a proficient Haskeller, but not for

an already terrified beginner.

Many times I've witnessed senior developers get very frustrated

when something wouldn't compile for hours and they couldn't find

any help to move forward: be prepared to assist them before they

get too grumpy. Some projects are better about it than other: Yesod

and Persistent have extensive documentation and the FPComplete crew

have numerous tutorials out there to help. New books come out once

in a while with fresher snippets: the time-tested Real World Haskell is now fairly outdated, but the more recent Beginning Haskell is perfectly relevant. Many channels on

IRC are available: #haskell-beginners, #haskell and #yesod,

although sometimes it can take work to get the answer you're

looking for. More than once I heard the comment that documentation

seems to be written by wizards for other wizards, and if you're a

lowly initiate, you will have a rough time.

I've personally had the privilege to help all of our developers

skill up in Haskell and Yesod, and I've become a huge believer in

the power of having someone more experienced guide you along the

way. What took me several months of learning, mostly by myself, now

takes our developers a couple of weeks of quality coaching. It took

me a while to grok monads, type classes, type families etc.,

however, properly guided developers can figure it out in a matter

of hours. Having a good teacher on your team will speed adoption

within the organization immensely.

Strength in numbers

We once experienced a very frustrating issue that got us thinking about our full commitment to Haskell as a company.

When we switched our main API to Yesod (a full rewrite), we

almost immediately ran into the issue the API would burn up close

to 95% of available CPU on whatever AWS EC2 instance it was hosted

on. We upgraded machines, just to see if we could cheat our way out

of fixing this by throwing money at the problem, and even with a

$600/mo 16 core box, the API still managed to flood all of the

available cores with barely any traffic hitting it. I personally

spent a good week banging my head against it: was it resource

contention? Was it a really big oversight in one of my handlers?

Was it misconfiguration? Was it something about the EC2

environment? Why doesn't this reproducing AT ALL under profiling?

Was it our database connection pooling? I threw a lot of

screenshots and code samples at the community both on Google Groups

and IRC: nobody else had ever seen anything like it. Uh oh.. All

the while customer support requests are pouring in, teachers are

aggravated, the team is looking at the devs and "their latest shiny

toy", tapping their collective foot.

This is the part where picking exotic tooling for your stack can

be a dangerous beast: "given enough eyeballs, all bugs are

shallow", and when only a dozen teams out there are using your

libraries at your scale, you are on your own when it comes to

fixing issues. With Rails, there's enough volume of developers that

there will be enough projects of every scale to burn-in your tool

of choice. That's simply not the case with Haskell's usage

numbers.

What this means is that if you're planning to bet the farm on

Haskell, you need to be ready and comfortable with the idea that

you might have to get your hands dirty, might be the first person

to figure out a solution to the problem you're seeing. This

requirement is pretty much non-existent in .NET / ruby / python at

al. Start small, start simple, let the tooling grow on you as you

gain experience. Start with tools that aren't mission critical

until you're more confident.

However..

It bears mentioning that the above concerns are being actively

addressed by the community and the state of things is rapidly

improving:

• Cabal, the Haskell package manager, was a real pain to work

  with just a few years ago and "cabal hell" is still part of Haskell

  vernacular. However, with sandboxes and consistent version

  snapshots provided by FPComplete as Stackage LTS, that problem has

  been mostly resolved.

• Build times are slow, but the community is coming up with

  improvements such as halcyon that should alleviate things

  considerably.

• Docs have gotten dramatically better over the past couple of

  years. There's been a big push towards keeping fresh,

  community-maintained, easy-to-follow and beginner-friendly

  instructions such as those provided by Chris Allen's Learn Haskell. We now even have IRC channels tailored specifically

  for beginners, e.g. #haskell-beginners . Today newcomers become

  more productive much faster than they did a few years ago.

• The community has been recently doing a better job at outreach

  and we've seen many new developers come make Haskell a permanent

  part of their toolbox. With more participants, tools get more

  fully-featured and more maintained.

Conclusion

It's a very exciting time in the history of computing to jump on

the Haskell train. Yes, the community is tiny and one might get

little hand-holding compared to more popular ecosystems, however

Haskell offers obvious benefits to software teams who can power

through the initial pain period.

Today Haskell offers some of the best tools around for

delivering quality software quickly and reliably, minimizing

maintenance cost while maximizing developer enjoyment. To me

Haskell is that dream of "developer happiness" that we were

promised many years ago by the Ruby community: I can write

beautiful, short, expressive and readable code that will perform

phenomenally and stand the test of time and continuous change. What

more can I ask for?