Mental modelling and programming talent

[Armed and Dangerous - Generative models and programming talent]

is ability to reason forward from causes like the construction of his loop to effects like the observed output is weak; his ability to reason backwards from desired output to the construction of the loop is nonexistent.

But for many people (I dare say for most people), they simply do not think of their program the way a programmer does. As a result, it is impossible for a programmer to explain to such a person how to find the problem in their code. I’m convinced after years of patiently trying to explain this to novices that most are just not used to thinking this way while a small group of other students seem to think this way automatically, without me having to explain it to them.

Reges later wrote up his account more formally as The Mystery of b := (b = false).

What is missing from Reges’s account of a “model of computation” is what the model held in a good programmer’s mind actually consists of: a rich set of causal relationships between possible states of the model. (But I am pretty certain Reges would agree with this elaboration instantly.)

Reges’s implicit theory is this: good programmers, and students who will become good programmers, have a generative model of computing. Poor programmers, and students who will become poor programmers, don’t. CS IQ consists of a talent for building generative models of computing.

Some recent work on the teaching of programming reinforce Reges’s point. See, for example, Improving the Viability of Mental Models Held by Novice Programmers. The authors, llike Reges, lack the notion of a generative model. But in considering how students succeed and fail, they note that students may hold different causal theories about the assignment operator in Java — and of course, only one of these theories is correct.

Another recent paper, The camel has two humps, draws a more general conclusion. In this one, two British researchers correlated responses on an exam used to filter incoming students aiming to study CS. They boldly claim to be able to predict a student’s success in CS courses before students have had any contact with any programming language.

I have seen this. Some people just do not think in a matter that is conducive to writing or debugging software. In fact, I believe it is more important for debugging than for just writing code.