PotW: Out of the Tar Pit

Wondering what PotW is? Check out my first Read Along.

This week’s Hacker School paper is Out of the Tar Pit by Ben Moseley and Peter Marks.

This paper discusses sources of complexity in programs. The paper is divided in two parts: the first part discusses types and flavors of complexity and the second part presents a system, which would enforce programmers to structure programs in a much simpler way.

In the first part authors divide complexity in two types: accidental and essential and argue that most of complexity is, in fact, accidental and we would be better off without it. They also give overview of common programming models (OOP, functional and logic) and their take on fighting complexity.

Complexity comes from two sources: (mutable) state and control. There are a lot of other sources, but they just consequences of these two.

This might sound very familiar or not, depends on your background. For me it does. I was constantly recalling Rich Hickey talks while reading this part, especially “Simple Made Easy”. You should watch it if you still didn’t. It is very good.

The second part was more interesting and novel to me. That’s were I experienced a couple of Whoa! moments when recognized some of the techniques that are implemented in existing systems. I believe that most of them didn’t consciously aimed to implement them, but retrospectively you can see a similar design decisions.

One example of this is popular library for building user interfaces called React. Essentially, it allows developers to treat state as global ground truth and specify how to render UI from it. It is very similar to the concept of treating your essential state as constant and deriving accidental state from it. Flux architecture style takes it one step further by introducing unidirectional flow. It resonate with the idea from the paper of restricting data flow between parts of the system that implement essential state, accidental state & control and user interaction stuff. Which makes reasoning about your program much simpler.

Another great library from the UI stack is DataScript which brings database into your browser. It is useful to represent your essential state in a way that don’t need to know anything about your query paths in advance. The paper’s system uses relational model for this, but the idea is the same.

For dessert, interesting citations from the paper.


So, what is the way out of the tar pit? What is the silver bullet? …it may not be FRP*, but we believe there can be no doubt that it is simplicity.

* FRP here means Functional Relational (not Reactive!) Programming

Words of Tony Hoare from his 1980 Turing award speech:

I conclude that there are two ways of constructing a software design: One way is to make it so simple that there are obviously no deficiencies and the other way is to make it so complicated that there are no obvious deficiencies. The first method is far more difficult.

And, as always, if you’re interested in gaining more rigorous understanding - go read the paper!