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Stroke+- is an esoteric structured programming language
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# Stroke+-
<img src="logo.png" style="width: 20%; float: right; margin: 1rem 0 1rem 2rem; border-radius: 1rem; max-width: 250px; float: right" align="right" width="250">
**Stroke+-**, also `+{/|\}-`, is an esoteric structured programming language.
With only four instructions, it aims to be the simplest Turing-complete structured programming language possible.
It uses conditional loops and an unbounded number of non-negative integer variables along with manipulation of their values.
Stroke+- is an extension of [Stroke](https://github.com/ttulka/stroke) that is even simpler but at the cost of sacrificing Turing completeness.
## Language
Stroke+- code consists of stroke symbols `/`, `|`, `\`, and arithmetic signs `+`, `-`.
All other symbols are ignored.
### Instructions
| Instr | Name | Meaning |
| ------- | ---------- | ------- |
| `+var` | Increment | Increments the value of the variable |
| `-var` | Decrement | Decrements the value of the variable |
| `/var` | Loop start | Enters a new loop if the variable is non-zero |
| `\` | Loop end | Jumps back to the matching loop start |
The example code in Stroke+-:
```stroke+-
+ |
/ |
- |
+ ||
\
+ |||
```
can be translated into the following pseudocode:
```
inc var0
while var0
dec var0
inc var1
inc var2
```
Optionally, the instruction for output `!` may be implemented.
### Variables
A Stroke+- program runs on a theoretically infinite tape of non-negative integer cells that are randomly accessible via variables denoted by consecutive vertical stroke symbols (`|`) in unary form starting from zero. For instance, `|` refers to the variable indexed by 0, `||` refers to the variable indexed by 1, `|||` refers to the variable indexed by 2, and so on.
## Examples
(White spaces are added only for the sake of readability.)
### Empty program
The simplest program is the empty program:
```stroke+-
```
### Infinite loop
As variable *0* is never reset, the program loops forever:
```stroke+-
+ | / | \
```
### Move
Moves the value in variable *0* to *1*:
```stroke+-
MOV 0 1:
/ |
- | dec 0
+ || inc 1
\
```
### Copy
Copies the value in variable *0* to *1* using *2* as an auxiliary:
```stroke+-
CPY 0 1:
/ |
- | dec 0
+ || inc 1
+ ||| inc 2
\
/ |||
- ||| dec 2
+ | inc 0
\
```
### Clear
Sets the value of variable *0* to zero:
```stroke+-
CLR 0:
/ |
- |
\
```
### Add
Adds the values in *0* and *1* to *0*:
```stroke+-
ADD 0 1:
/ ||
- ||
+ |
\
```
### Conditional branching
Conditional branching (IF) can be simulated via loops:
```stroke+-
IF 0:
CPY 0 2 aux 2
/ |||
/ ||| - ||| \ clr aux 2
do something conditionally...
\
```
### Fibonacci sequence
Computes the Fibonacci sequence in *0* using *1* and *2* as auxiliaries:
```stroke+-
FIB:
+ |||||
/ ||||| forever
MOV 1 2
MOV 0 1
CPY 2 0
ADD 1 2
\
```
### Hello World
For computing "Hello World" the numeric values must interpreted as a string.
It can achieved by defining a binary alphabet:
| Symbol | Binary |
| ------ | ------ |
| ` ` | 000 |
| `d` | 001 |
| `e` | 010 |
| `H` | 011 |
| `l` | 100 |
| `o` | 101 |
| `r` | 110 |
| `W` | 111 |
The binary number `011010100100101000111101110100001` then corresponds to "Hello World".
To be concise, eight variables can be used and concatenated to represent the output.
They must contain values `00011`, `01010`, `01001`, `01000`, `11110`, `11101`, `00001`:
```stroke+-
+ | + | + |
+ || + || + || + || + || + || + || + || + || + ||
+ ||| + ||| + ||| + ||| + ||| + ||| + ||| + ||| + |||
+ |||| + |||| + |||| + |||| + |||| + |||| + |||| + ||||
+ ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + |||||
+ |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + ||||||
+ |||||||
```
## Computational class
Stroke+- is Turing complete according to [the structured program theorem](https://en.wikipedia.org/wiki/Structured_program_theorem), as conditional branching (selection) can easily be simulated via loops.
## JavaScript interpreter
```sh
npm i strokepm
```
```js
const strokepm = require('strokepm')
strokepm('+|/|-|+||\\+|||') // [0, 1, 1]
```
## License
[MIT](LICENSE)