There are a lot of computer languages. While there are some pretty striking differences between the above, they all have two things in common. They all involve controlling a computer by writing lines of code, and they were all invented to be useful.
There is another category of language that is not burdened by that second attribute. Useful? Pf. Not bound by the constraints of utility, the whole ‘lines of code’ thing often ceases to apply as well. These non-utile outliers fall under the general category of “esoteric language”, sometimes shortened (but not by me) to esolang.
While I have long been peripherally aware of this category of languages, in a small email discussion recently a friend of mine mentioned the language Brainfuck (sometimes written b****fuck to avoid offending people). Another member of the discussion linked to an amusing top-ten list of odd languages. I read the article and my brain started fizzing.
A programming language that is written as a musical score? Blocks of color that simultaneously convey quantity and program flow*? A program specifically designed to be as difficult as possible to write code in?
Some might ask, “why would anyone bother with such useless languages?” I don’t have an answer to that. I could go on about Befunge and the wire-cross theorem, or about Turing Completeness, but at the end of the day, I think it’s the same answer as one might give to the question “why does one bother writing poetry, when prose is so much clearer?”
Some of the languages are just for fun. INTERCAL (Compiler Language with No Pronounceable Acronym) set out with only one goal: to not be like any other language. For instance, since all coders have long been taught to avoid the GO TO command, INTERCAL instead uses COME FROM. And every now and then you have to say PLEASE. You don’t have to be a geek (but it helps) to enjoy this article about INTERCAL and Befunge (includes a Befunge program to generate Mandelbrot sets).
One can only read about esoteric languages for so long before one must scratch the itch and find a new way to write “Hello, World!” on a screen. I became intrigued by Befunge, a language that is not written as lines of code at all, but as a grid that a pointer moves around on, steered by >,<,^, and v characters. The program appealed to me for two key reasons: the characters the program cursor encounters can mean different things depending on which direction the cursor is moving at the time, and, even better, you can have the program alter itself by changing the characters in the playfield.
So, here's my Hello, World! in Befunge:
095*0 v 0*59 <
This 'Hello World' program is written in Befunge, a
language invented expressly to be as difficult to compile
In fact, with this code, control flow goes straight through
this block of text and uses the p in 'program' as an instruction.
v g0*59 < 1
> "0"+292*p > "l",^
> :6*9- :9`!|
>:2-!| > $ ^
> 7"0"+273*p "o",^
> " ",^
Of course, it was absolutely required that the code alter itself at least once, and occasionally have the same symbol mean different things. This program is based on a counter, and when the counter is 0, it outputs an 'H'. When the counter is at 1, out comes an 'e'. 'l' is a little more complicated; after it matches the 2, the program does a little algebra (6x-9) to come up with 3, with which it then overwrites the 2 in the code. That way, on the next loop, when the counter is 3, we get another 'l', and the same equation replaces the 3 with a 9, ready for the 'l' in 'World'.
In the language, ! means 'not'. At the very bottom, this code evaluates the ! as 'not', which causes the program to loop around and pass through "!" (with quotes), turning what had been a program instruction into the exclamation point at the end of "Hello, World!" A nice little exclamation point on my program, as well.
The astute will recognize the place where an error output should occur, but currently doesn't.
Wooo! Big fun! While this language is nearly useless for actually accomplishing anything, I like the way you can make your code physically resemble the problem you are solving. A coworker mentioned writing a tic-tac-toe program with Befunge, and I immediately thought of building a program that is a grid of nine segments and the program alters the paths through the grid as moves are made. It would be awesome.
If I went back to college and majored in computer science, I could get credit for writing it.
In my wanderings, there was one program that completely blew my mind. You remember Brainfuck? There are only eight commands in that language, which makes it relatively simple to write an interpreter. An interpreter is a program that reads the code and executes the instructions as it encounters them, translating them from the (allegedly) human-friendly programming language into machine-friendly instructions for that particular processor. (Compilers do all the translating at once, before the program is executed, while interpreters do it on the fly.)
So here, ladies and gentlemen, is a Brainfuck interpreter, written in another esoteric language, Piet:
(courtesy Danger Mouse — if I'm not mistaken, the inventor of Piet)
That picture right there? That's a program, written in a Turing-complete language, that implements another Turing-complete language. (**)8-O (the sound you heard was my head exploding.)
* In Piet, you can write a program to calculate pi that is a circle.