Lorin software December 21, 2020December 21, 2020

3 Minutes

With apologies to Ken Iverson.

Architects draw detailed plans before a brick is laid or a nail is hammered. Programmers and software engineers don’t. Can this be why houses seldom collapse and programs often crash?

Blueprints help architects ensure that what they are planning to build will work. “Working” means more than not collapsing; it means serving the required purpose. Architects and their clients use blueprints to understand what they are going to build before they start building it.

But few programmers write even a rough sketch of what their programs will do before they start coding.

Leslie Lamport, Why We Should Build Software Like We Build Houses

“My instinct is to go right to the board. I’m very graphic oriented. I can’t talk more than ten minutes without I [sic] start drawing pictures when we’re talking about the things I do. Even if I’m talking sports, I invariably start diagramming what’s going on. I feel comfortable with it or find it very effective.”

This designer, like the newly promoted engineer at Selco who fought to get her drafting board back, is pointing out his dependence on the visual process, of drawing both to communicate and to think out the initial design. He also states that the visual and manual thought process of drawing precedes the formulation of the written specifications for the project. Like the Selco designers and those at other sites, he emphasized the importance of drawing processes to work out ideas. [emphasis added]

Kathryn Henderson, On Line and On Paper: Visual Representations, Visual Culture, and Computer Graphics in Design Engineering

The quote above by Kathryn Henderson illustrates how mechanical engineers use the act of drawing to help them work on the design problem. By generating sketches and drawings, they develop a better understanding of the problem they trying to solve. They use drawing as a tool to help them think, to work through the problem.

As software engineers, we don’t work in a visual medium in the way that mechanical engineers do. And yet, we also use tools to help us think through the problem. It just so happens that the tool we use is code. I can’t speak for other developers, but I certainly use the process of writing code to develop a deeper understanding of the problem I’m trying to solve. As I solve parts of the problem with code, my mental model of the problem space and solution space develops throughout the process.

I think we use coding this way (I certainly do), because it feels to me like the fastest way to evolve this knowledge. If I had some sort of equivalent mechanism for sketching that was faster than coding for developing my understanding, I’d use it. But I know of no mechanism that’s actually faster than coding that will let me develop my understanding of the solution I’m working on. It just so happens that the quickest solution, code, is the same medium as the artifact that will ultimately end up in production. A mechanical engineer can never ship their sketches, but we can ship our code.

And this is a point that I think Leslie Lamport misses. I’m personally familiar with a number of different techniques for modeling in software, including TLA+, Alloy, statecharts, and decision tables. I’ve used them all, they are excellent tools for reasoning about the complexity of the system. But none of these tools really fulfill the role that sketching does for mechanical engineers (although Alloy’s fast feedback for incremental model building is a nice step in this direction).

TLA+ in particular is a wonderful tool. I’ve used it for things like understanding the linearizability paper, beating the CAP theorem, finding cycles in linked lists, solving the river crossing problem, and proving leftpad. But if you’re looking for an analogy in mechanical engineering, TLA+ is much closer to finite element analysis than it is to sketches.

Developers jump to coding not because they are sloppy, but because they have found it to be the most effective tool for sketching, for thinking about the problem and getting quick feedback as they construct their solution. And constructing a representation to develop a better understanding using the best tools they have available for the job to get quick feedback is what engineers do.