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Cognitive load is what matters

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1455 points nromiun | 1 comments | 30 Aug 25 12:58 UTC | HN request time: 0s | source
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exclipy ◴[30 Aug 25 20:51 UTC] No.45077894[source]▶
This was my main takeaway from A Philosophy Of Software Design by John Ousterhout. It is the best book on this subject and I recommend it to every software developer.

Basically, you should aim to minimise complexity in software design, but importantly, complexity is defined as "how difficult is it to make changes to it". "How difficult" is largely determined by the amount of cognitive load necessary to understand it.

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tverbeure ◴[30 Aug 25 22:57 UTC] No.45078728[source]▶
Only half joking: I don’t think I trust a book from an author who has inflicted decades of TCL pain on me (and on the entire community of EDA tool users.)
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1. RossBencina ◴[31 Aug 25 02:10 UTC] No.45079711[source]▶
I know you're only half joking, but I don't think you can pin the blame on John or TCL. Osterhaut's thesis, as I recall, was that there is real benefit to having multiple programming languages working at different levels of the domain (e.g. a scriptable system with the core written in a lower level language). Of course now this is a widespread practice in many domains (e.g. web browsers, numerical computing: matlab, numpy). It's an idea that has stood the test of time. TCL is just one way of achieving that aim, but at the time it was one of few open-source options available. I think scheme/lisp would have been the obvious alternative. AutoDesk went in that direction.

I remember using TCL in the 90s for my own projects as an embeddable command language. The main selling point was that it was a relatively widely understood scripting language with an easily embeddable off-the-shelf open source code base, perhaps one of the first of its kind (ignoring lisps.) Of course the limitations soon became clear. Only a few years later I had high hopes that Python would become a successor, but it went in a different direction and became significantly more difficult to embed in other applications than was TCL -- it just wasn't a primary use case for the core Python project. The modern TCL-equivalent is Lua, definitely a step up from TCL, but I think if EDA tools used Lua there would be plenty of hand-wringing too.

Just guessing, but I imagine that at the time TCL was adopted within EDA tools there were few alternatives. And once TCL was established it was going to be very hard to replace. Even if you ignore inertia at the EDA vendors, I can't imagine hardware engineers (or anyone with a job to do) wanting to switch languages every two to five years like some developers seem happy to do. It's a hard sell all around.

I reckon the best you can do is blame the vendors for (a) not choosing a more fit-for purpose language at the outset, which probably means Scheme, or inventing their own, (b) or not ripping the bandaid off at some point and switching to a more fit-for-purpose language. Blaming (b) is tough though, even today selecting an embedded application language is vexed: you want something that has good affordances as a language, is widely used and documented, easily embedded, and long-term stable. Almost everything I can think of fails the long term stability test (Python, JavaScript, even Lua which does not maintain backward compatibility between releases).