Comment by FartyMcFarter
4 days ago
I don't know much about CSS, but Turing completeness is notorious for showing up in systems unintentionally.
It doesn't take much to be Turing-complete - if a system provides unbounded read/write memory plus branching or conditional recursion you're usually there.
As an example, Magic The Gathering (the card game) is Turing-complete: https://arxiv.org/abs/1904.09828 . You can use creature tokens as memory and various game mechanics to do flow control. Was this intentional by the designers? Most likely not...
* MOV x86: using memory mapped lookup tables, you can simulate logic gates and branching using only MOV.
* PowerPoint (Without Macros): using On-Click Animations and Hyperlinks, shapes on slides act as the tape and clicking them triggers animations that move the head or change the state of the slide.
* find and mkdir (Linux Commands): find has a -execdir flag executes commands for directories it finds. By using mkdir to create specific folder structures, you can create a feedback loop that functions as a Tag System (aka universal computation).
* Soldier Crabs: Researchers showed that swarms of Mictyris guinotae can be funneled through gates to implement Boolean logic. While a full computer hasn't been built with them, the logic gates (AND, OR, NOT) are the building blocks for one.
Even water is Turing Complete:
* Fluidic Logic Gates: the Coandă effect is the tendency of a fluid jet to stay attached to a convex surface. By using tiny air or water jets to push a main stream from one channel to another, you can create the fluid equivalent of a transistor.
* MONIAC (Monetary National Income Analogue Computer)
* Navier-Stokes equations describe how fluids move are TC.
* In 2015, Stanford researchers developed a computer that operates using the physics of moving water droplets. Tiny iron-infused water droplets moved by magnetic fields through a maze of tracks. The presence or absence of a droplet represents a 1 or a 0. By colliding or diverting each other, the droplets interact perform calculations.
> Turing completeness is notorious for showing up in systems unintentionally
Greenspun's 10th law.
https://wiki.c2.com/?GreenspunsTenthRuleOfProgramming
That's on the opposite end of the complexity spectrum.
Perhaps so, but ISTM that it encapsulates the same basic point. Try to make something rich and general and you often end up re-implementing a whole computer inside your computer.
Which is why these days it's easier in many cases to just embed an Arm core and implement your controller's functionality in software.
1 reply →