– question from a young programmer
So, does functional programming stack up in the real world? In industry?
Yes. Check my linkin profile. I have been programming, in industry, as long as you have been alive.
Here are some (pure) functional programming examples to back up this claim, because academics can talk all they want, but they are not in there, in the trenches, with you where it counts.
I am, because I happened to have dug a few of those trenches. You're welcome.
Case study 1: ATS-L
Worked on a project in DHS called 'ATS' ('Automated Targeting System'). The existing system ATS-C was a 100,000-line Prolog behemoth that used pure dynamic types (no type hints, nor boxed types) and every rule started with an assert and ended with a retract. And 100,000 lines.
It was impossible to know what was going on in that system, without running the code in the debugger and pulling from the dynamic environment. Consequently, the ATS-C guy had (still has) job security. Not his aim, but that is a nice plus.
It took us 72-hours to go through every line of his code to correct the Int-rollover problem when the primary key exceeded two billion for the index.
So, I was called in to 'help.' HA! But then eventually I built ATS-L. I wrote it in 10,000 lines of purely functional Prolog (yes, that is possible to do, and remain authentic to logic programming in Prolog), so every rule called gave the same truth-verification from the same set of arguments, every time.
Shocker! I know.
I had the same level of functionality of ATS-C and handled 1,000x the number of transactions per hour. And as it was purely functional Prolog, I could reason about my program in the large and in the small. Importantly, so could others, as I passed on that work after maintaining it for three years.
In short: 1/10th the SLOC with the same level of functionality with increased real-time responsiveness and a vastly reduced level of maintenance.
Oh, and I also wrote 726 unit tests and put them on an automated midnight run, generating a report every single day. If my system broke, or something changed, I knew it, and management knew it when the report was automatically emailed to them.
Case Study 2: CDDS
Worked three years in Fannie Mae devising within a team an appraisal review process, CDDS. We had a good team of five engineers and I was given the 'Sales Comparison Approach' which had 600 elements out of 2,100 data elements in over 100 data tables, one of the tables ingested 100 million elements per month. All the elements were optional. All of them, so primary key dependencies were an ... interesting problem. The upshot was that Sales Comparison Approach was an impossible task to code, as we coded it in Java, of course.
What did I do? I coded it in Java.
After I implemented the Maybe type, then the Monad type-class ... in Java.
After I completed the system and tuned it, storing only the values that were present in the submitted forms, my manager reported up the chain that SCA and CDDS would have failed if I had not been there to implement it.
How did I implement it? In Java. I didn't use one for-loop and my if-statements were not there. I used the Maybe-Monad to model semi-determinism, lifting the present data to Just x and the absent data ('null') to Nothing, and then I executed action against the monadic data.
Simple. Provable. Implemented. Done.
Oh, and I had written 1,000 of the 1,100 unit test cases. SCA had 1,000 unit test cases, the rest of the system had a total of 100 unit test cases.
My code coverage was fiiiiiiine.
Case Study 3: Sunset Dates
This one was interesting.
I worked at Freddy Mac for a year, and they had a problem, and that problem was to calculate the sunset date for a mortgage based on the most recent date from one of possibly five indicators, that changed with each possible mortgage transaction.
Three different software teams tackled this problem over a period of six months and none of them implemented a system that passed UAT.
I sat down with the UATester and kept getting part of the story. I lifted our conversations up into the categorical domain, and then dropped that into a Java-implementation (I used both monads and comonads which I had implemented).
It took me two solid months working with this tester and a front-end developer, but we passed UAT and we got the customer and their SMA to sign off on it.
Three person team, purely functional programming ... in Java won that work where standard imperative approaches failed, over and over again.
Funny story. I was seriously asked on that project: "What's a tuple?"
Case Study 4: Dependency Graphs of Program Requirements ('TMQER')
I can't compare what I wrote, in Haskell, to an alternative system, because the alternative, traditional imperative approach was never essayed. We had a set of 521 requirements for a program with many (multiple) parent and child dependencies, so it wasn't a tree, it was a graph. So, I parsed the requirements document into a Haskell Data.Graph and provided not only a distance matrix, as requested (which is not what the customer wanted at all: it was just what they said and thought they wanted), but also clustering reports of which requirements were the 'heaviest' having the most dependencies and which requirements were show-stoppers to how many follow-on requirements.
Then I uploaded my Haskell Graph into Neo4J, making heavily-clustered requirements an obvious visual cue. And we won that contract.
The project wasn't attempted in Java. The project was attempted in R, and it couldn't be done. They estimated the graph manipulation algorithm would be 200-lines of code in R, that they couldn't get working.
With comonads, I did it in one line of Haskell. One line for a graph deforestation algorithm to get to the bare essentials of what was important to the project. Wanna see it?
How hard was that? In Haskell, a pure functional programming language, not hard at all.
Not only that, that we won a contract that our competing companies said was impossible, but our VP got wind of this and started vetting my tech to other companies.
We have a contract in the works, right now, using Haskell and Neo4J on AWS that is answering questions about fuzzy relations in social networks that a company that is expert in social engineering needs us to answer.
And I can answer these questions using graph theory and purely functional programming.
Case study 5: the one that got away
Oh, and then there was the one that got away. It had to do with a neural network I built in Mercury, a purely functional logic programming language with Prolog-like syntax that was able to classify images into 'interesting' and (mostly) 'not-interesting' but 'interesting' had very specific, different meanings, and it was able to classify these images, using a pulse-coupled neural network, in ways that eliminated 99% of waste images quickly so that analysts could concentrate on doing work, as opposed to sieving through the deluge of useless images to get the the ones they needed to see.
I build a working prototype and demoed it.
This had never been done before. Ever.
Then, a Big Six came in and said, 'we can do that for you with 250 programmers and Java' and stole the project. After ten years and billions of dollars, they were unable to reproduce my work.
Pure Functional Programming Claims IRL
So, let's do a real-money tally.
ATS-L in one month, in the three years I maintained it (it is still up and running ten years later, ladies and gentlemen) made $26 million dollars in seizures and rescued three teens being human-trafficked over the border.
CDDS has been in production since the year 2010 and has verified appraisals helping Fannie Mae to make 62 Billion dollars in net profit in one quarter the year it went live, actually contributing to the rescue of Fannie Mae from insolvency.
TMQER has rescued a government run program from failure that has the funding price-tag of over 100 Million dollars of Government (your) taxpayer (your) money. You're welcome.
Sunset dates I wish I had a dollar amount, but you can estimate for me: three teams of business analysts and software engineers over a six month period said it couldn't be done (or tried it and failed). I scrapped all that code, wrote the system from first principals (Category Theory) and got it working and approved in two months. You do the math.
... Oh, and then there's my current project. I might actually be able to own this thing. Hmmmm.
So, yes, Virginia,
1. there is a Santa Clause
2. those academics are actually onto something. (Pure) functional programming actually does matter. It actually does allow you to program better, faster and more cleanly, and with these enhanced skill-sets you become the one they turn to when other teams throw up their hands at an 'impossible' task. And then you deliver, ahead of expectations on both time to deliver and budget costs.