<>^v

<>^v is a stack-based language that allows moving the instruction pointer in two dimensions. All commands except strings and numbers are one character long so that the program can easily be written to work in multiple directions.

Version 2 (with thread and functions) is currently in development.

The instruction pointer by default starts at (0, 0) and goes towards the right. However, you can change its starting position by using the @ character. The last @ (left-to-right, then up-to-down, like reading direction) will be used to specify pointer position if there are more than one. The program is halted when the instruction pointer gets to the end of a line or column or when it encounters a !.

There is an integrated (very basic) turtle support. Supported commands are forward, backward, turn left, turn right, set speed, toggle turtle visibility, set window title, toggle pen (up / down) and handling of keyboard arrows via GOTOs.

When using turtle with event handling, you should (after executing program tasks and at the end of event handlers) send the program into an infinite loop to prevent it from exiting.

Running Online

If you want to run a <>^v program online, use this tool I made to run code on a remote server.

Basics

The language is stack-based. The stack can grow very large (up to the Python implementation's maximum array length). There is also variable space, where you can store values in a way that will not be modified when pushing new values to the stack. Any character that is considered a letter except v (including letters with diacritics) can be used as variable name.

Push a number to the stack

To push a number onto the stack, just write it. There is no maximum of leading zeroes. Floating point number literals are not currently supported.

Push a string to the stack

To add a string to the stack, use "string".

IMPORTANT : Number and strings can be written in any of the four directions.

Strings and numbers are read character by character by the instruction pointer, in the direction it is going. So "woem" can be interpreted as meow if the pointer is coming from the right.

Controlling the instruction pointer

The instruction pointer has a direction, which is by default left to right. It can be changed by the following characters :

• > tells the pointer go right. It is ignored if the pointer is going left.
• < tells the pointer go left. It is ignored if the pointer is going right.
• ^ tells the pointer go up. It is ignored if the pointer is going down.
• v tells the pointer go down. It is ignored if the pointer is going up.
• | is a mirror. When reached, it inverts the pointer's direction.

Control statements (or something like that)

• = is the equality operator. It only executes the character immediately after it if the top two elements of the stack ae equal.
• ‹ and › (or { and }) work like =, but it tests instead first element of the stack ‹ | › second element of the stack.
• ≤ and ≥ (or [ and ]) work like ‹ and ›, but they test greater or equal or lesser or equal.

Operators

• * sets the top of the stack to the top of the stack * second element of the stack
• + sets the top of the stack to the top of the stack + second element of the stack
• - sets the top of the stack to the top of the stack - second element of the stack
• / sets the top of the stack to the top of the stack / second element of the stack
• ⁄ sets the top of the stack rounded result of to the top of the stack / second element of the stack

Warning : key event handlers support is not always working.

Examples

Hello World

"Hello World!";

Infinite loop

>v
^<

Prime number tester (prime.udlr or online version)

>,tTT2]!2i>IT%0=vIT[vv
ù                 > vv
"               I   TI
                T   ~)
>               =    i
r               > ^  v
e         ^          <
b                   v
m               ~   >" is "v
u               >" is not ">~"prime";
n
"
^@|

Event handling

This example allows the user to control the turtle via the arrow keys (movement.udlr).

1∑0 3¡_4€_5£_6∞¢v
            v<  <
            >^
5∑          ¶^
0 10-æ      ¶^
5ß          ¶^
0 10-ª      ¶^

Interpreter usage

First, make udlr.py executable : chmod +x ./udlr.py

Then, you can use it this way : ./udlr.py filename.udlr

On Windows (or if you do not want to chmod +x udlr.py) : python3 ./udlr.py filename.udlr

An optional --debug argument can be passed to the interpreter after the file name.

./udlr.py filename.udlr --debug

If that argument is passed, all instructions will be printed when executed and prints to standard output will be prefixed by PRINT .

---

Commands

Command	Description
>	instruction pointer right
<	instruction pointer left
v	instruction pointer down
^	instruction pointer up
|	mirror - reverse instruction pointer
!	exit
<num>	push num to the stack
;	print top of the stack
&	print stack
,	input number and push to the stack
.	input string and push to the stack
*	multiply top element of the stack by second-top element of the stack
/	divide top element of the stack by second-top element of the stack
+	add top element of the stack to second-top element of the stack
-	substract second-top element of the stack to top element of the stack
%	modulo - set top of stack to [top of stack] % [second-top element of the stack]
=	if equal - skip next instruction if top two elements of the stack are not equal
:	if not equal skip next instruction if top two elements of the stack are equal
}	skip next instruction if top element of the stack is greater than second-top element of the stack
{	skip next instruction if top element of the stack is smaller than second-top element of the stack
]	skip next instruction if top element of the stack is greater or equal to the second-top element of the stack
[	skip next instruction if top element of the stack is smaller or equal to the second-top element of the stack
_	pop stack
<chr>	pop stack and write to slot chr
<CHR>	push slot chr to stack
\	print ASCII char corresponding to top of stack
~	print top of stack without newline
¬	print variables
"<STR>"	push string to stack
)	increment top of stack
(	decrement top of stack
~	print top of stack without newline
V	throw error
«	goto y = top of stack x = second element of stack and set instruction pointer to default
»	run file - run file [third element of stack] with pointer starting at y [top of stack] x [second element of stack]
?	swap top two elements of stack
`	print newline
#	push random number between 0 and [top of stack] to stack
°	wait for 0.1 second
@	instruction pointer will start here
√	set top of stack to square root of top of stack
◊	set top of stack to [second element of stack]-th root of top of stack
†	set top of stack to [top of stack]^2 (shortcut for adding 2?^ or having 2 already on the stack and calling ^)
…	convert top of stack to number
‹	same as {
›	same as }
≥	same as ]
≤	same as [
⁄	integer division (top of stack // second element of stack)
ù	special variable ; if set, the , and . commands will use its value as prompt
§	push to stack all elements of top of stack.split(second element of stack) and push number of elements
¯	push to stack (top element of stack).substring(second element of stack, third element of stack)
±	toggle sign of top of stack
≈	duplicate top of stack
Ω	fetch url [top of stack] ; push page contents
‡	top of stack = str(top of stack)
¥	remove second element of stack, shortcut for ?_
•	push index of [top of stack] in [second element of stack]
¿	push length of top of stack
–	(not a minus) string reverse - reverse top of stack
®	set top of stack to (get character (top of stack) of [second element of stack])
∑	turtle - forward by [top of stack]
ß	turtle - backward by [top of stack]
æ	turtle - turn left [top of stack] degrees
ª	turtle - turn right [top of stack] degrees
œ	turtle - set speed to [top of stack]
µ	turtle - set window title to [top of stack]
ƒ	turtle - toggle turtle visibility
¢	turtle - listen to events and set handlers for arrow keys
¡	(inverted !) turtle - set up arrow handler to (GOTO y [top of stack] x [second element of stack] ; reset instruction pointer direction to default)
£	turtle - set down arrow handler to (GOTO y [top of stack] x [second element of stack] ; reset instruction pointer direction to default)
€	turtle - set left arrow handler to (GOTO y [top of stack] x [second element of stack] ; reset instruction pointer direction to default)
∞	turtle - set right arrow handler to (GOTO y [top of stack] x [second element of stack] ; reset instruction pointer direction to default)
∆	turtle - raise or lower pen (toggle state)
π	turtle - reset screen and position
¶	turtle - update screen (push updates to screen)