Stroke+-

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 which 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+-:

+ | 
/ | 
  - | 
  + || 
\ 
+ |||

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:

Infinite loop

As variable 0 is never reset, the program loops forever:

+ | / | \

Clear

Sets the value of variable 0 to zero:

CLR 0:
/ |
  - |
\

Move

Moves the value in variable 0 to 1:

MOV 0 1:
/ |
  - |     dec 0
  + ||    inc 1
\

Copy

Copies the value in variable 0 to 1 using 2 as an auxiliary:

CPY 0 1:
/ |
  - |     dec 0
  + ||    inc 1
  + |||   inc 2
\
/ |||
  - |||   dec 2
  + |     inc 0
\

Add

Adds the values in 0 and 1 to 0:

ADD 0 1:
/ ||
  - ||
  + |
\

Conditional branching

Conditional branching (IF) can be simulated via loops:

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:

FIB:
+ |||||
/ |||||    forever
  MOV 1 2
  MOV 0 1
  CPY 2 0
  ADD 1 2
\

Hello World

For computing "Hello World" the numeric values must be 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:

+ | + | + |
+ || + || + || + || + || + || + || + || + || + ||
+ ||| + ||| + ||| + ||| + ||| + ||| + ||| + ||| + |||
+ |||| + |||| + |||| + |||| + |||| + |||| + |||| + ||||
+ ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + ||||| + |||||
+ |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + |||||| + ||||||
+ |||||||

Computational class

Stroke+- is Turing complete according to the structured program theorem, as conditional branching (selection) can easily be simulated via loops.

JavaScript interpreter

npm i strokepm

const strokepm = require('strokepm')

strokepm('+|/|-|+||\\+|||')  // [0, 1, 1]

License

MIT