Personal experience: Cognitively effortful, interesting to work with. I've programmed a TM that finds the n-th prime. Turing Machines are necessary to understand some arguments in Paul Cohen's *Set theory and the continuum hypothesis*. More recently, [here](https://www.scottaaronson.com/blog/?p=2725) is a Turing Machine which halts iff ZFC is inconsistent.
Personal experience: One of the first programming languages I learnt, and thus my documentation was in Spanish. I've used it to crunch numbers when a speedup mattered. I've also used it in ways it wasn't meant to: to program a database application, to analyze a lexical corpus, to solve riddles. This has led me to appreciate higher languages more, and to understand them better. For example:
In JavaScript, consider the function:
```
function reverseArrayInPlace(array) {
for (let i = 0; i <Math.floor(array.length/2);i++){
let old = array[i];
array[i] = array[array.length - 1 - i];
array[array.length - 1 - i] = old;
}
return array;
}
```
This function reverses an array, and changes it. However, the scope of the array which the function manipulates is local, and yet the original array is changed. This is because, although JavaScript doesn't work with pointers, it is working with pointers, and the local copy of the pointer is pointing to the same place.
Having had to deal with memory allocation, working in a language which just deals with it is orgasmic.
Representative project: [Machine Learning Demystified](https://nunosempere.github.io/maths-prog/MachineLearningDemystified/). In which I fall in love with sklearn, a popular machine learning library for Python.
Personal experience: I view this language with a lot of affection, and I like it a lot; I have found analyzing datasets to be very cognitively stimulating. The ggplot2 library is amazing. The time required to create a new program is basically 0, in RStudio, because you don't really compile the whole program at once, but instruction by instruction / line by line. Would recommend. Ultimately, when working with huge datasets, what one does is to load a library which has functions written in C.
Personal experience: I learnt PHP to program the above webpage. Ultimately, however, I could have just used JavaScript, because I don't really needed a database / everything could have been computed on the user's side. Demistifyies some webpages.
Personal experience: When I first wrote this, reading Chapter 5 of *Eloquent JavaScript*, [Higher order functions](https://en.wikipedia.org/wiki/Higher-order_function) had just clicked for me. In hindsight, I had already used lapply in R, and functions which modify other functions are pretty natural in Haskell, but I had the Eureka moment. Later, I used JavaScript to implement approval voting for the Center for Eletion Science, and will further use it to contribute to foretold.io, a forecasting platform.
Unix shell, Matlab. Honorable mention to JSFuck for its practical uses. Honorable mention to Intercal for the following paragraph, which has stayed with me:
> Until the new INTERCAL compiler with better RYM[6] access comes out, the old compiler has no way of knowing which language you are familiar with and thus it doesn't know what language to produce its output in[7]. INTERCAL elegantly solves this problem by producing its output in Roman numerals, under the assumption that when Rome was at the height of its strength, half the world was under its dominion, so the comprehension of Roman numerals is part of our racial memory.
Update: It has since been pointed out to me that Latex, HTML and MySQL might be Turing complete. This is not the first time that I've encountered an unexpected Turing; the game *Magic The Gathering* also turns out to belong to this category. I feel that this fact contains a deep lesson about the structure of the world, though it escapes me at the moment.
Personal experience: Templates are not evil; they're the difference between [shapleyvalue.com](shapleyvalue.com) and [easyfirma.es](easyfirma.es). Easy to pick up. Also easy to clutter.
## MySQL / MariaDB
Representative project: None as of yet.
Useful for: Databases on the server's side.
Personal experience: Pretty straightforward; it's not even Turing complete. I prefer MariaDB on principle, because it's Free (Libre!) Software.
