README.md

Custom Logo language

Logo com.interpreter presented here is just another implementation of popular Logo language.
During work, we took inspiration from:
Lynx a modern, online version of logo with many additions as animations, multiple turtles etc.

Graphical User interface

Commands view consists of:

• logo canvas where user can see code execution
• history of pressed commands
• navigation buttons
  • Commands button - go to Commands view (at picture above)
  • Procedures button - go to procedure view (at picture below)
  • Variables state - go to Variable state view
  • Load file - load ready file to programme
  • Clean button - clean environment (procedures and variables)
  • Stop button - stop current execution
• command prompt to write commands (Enter to execute)
• error box where errors will be displayed

Procedures view is very similar to Commands view - the main difference is command prompt and command history is replaced with simple editor and button executing the programme written in the editor.

Variable state displaying all current variables with values and all stored procedures.

Language list of commands:

Name	Description	Syntax
forward	Move current turtle forward	forward 100 fd 50+40
back	Move current turtle back	backward -10 bc 50-40
left	Turn current turtle left	left 90 lt 45
right	Turn current turtle right	right 90 rt 45
repeat	Perform block of instruction set number of times	repeat 2 [ fd 20 lt 90]
while	While loop	while 1 [ fd 20 rt 90]
assign	Assign value to the variable	assign :x 100
let	Creates a variable with specific value or overwrite it	let ::x 100
changeTurtle	Change turtle from one to another	changeturtle tt
clean	Clean the canvas	clean
home	Set current turtle to start location (0,0)	home
if	If instruction - with no else	if :x>10 { forward 100 left 90}
ifElse	IfElse instruction - else is compulsory to specify	ifElse :x>10 [fd 100] [back 100]
newTurtle	creates a new turtle with specified name	newturtle tt
penDown	Put the pen down - turtle is drawing line when walking	pd
penUp	Put the pen up - turtle is not drawing while walking	pu
call	Call a specified procedure	call square :x
procedure	Creates a procedure	procedure square :x { repeat 4 [ fd :x left 90]}
removeTurtle	Removes turtle	removeturtle tt
rename	Change current turtle name	rename ttt
setColor	Set current turtle pen color	setcolor 7
setPenSize	Set current turtle pen size	setpensize 5

Comments

To write commends use: # comment here #
Comments need to be open and closed and could take many lines.

Math expression:

Language enables writing mathematical expression for example:
(2+2)*2 will evaluate to 8 and 2+2*2 will evaluate to 6.
When writing operator that takes two arguments put it between them:
2 pow 7 is correct, while:
pow 2 7 will give an error.

List of mathematical expressions:

Name	Value	Alternative values	Description
abs	abs	ABS	Absolute value
arctan	arctan	ARCTAN	Arcus tangent from value
cos	cos	COS	Cosine function
int	int	INT	Cast value to integer
ln	ln	LN	Natural logarithm
minus	-		Minus sign
random	random	RANDOM	Random number between 0 (inclusive) and specified value (casted to int and exclusive)
round	round	ROUND	Round value to integer
remainder	remainder	REMAINDER, %	Modulo
sin	sin	SIN	Sinus function
sqrt	sqrt	SQRT	Square root of value
tan	tan	TAN	Tangent function
not	not	NOT, !	Logical not
power	pow	POW, ^	Power of two numbers 10 pow 2 is equal 100
sum	+		Sum of two values
product	*		Product of two values
division	/		Division of two values
different	!=		Not equal
equals	==		Equal
bigger	>		Bigger relation
smaller	<		Smaller relation
bigger or equal	>=	=>	Bigger or equal relation
smaller or equal	<=	=<	Smaller or equal relation
exp	exp	EXP	Exponential function equals to POW with e as exponent
log	log	LOG	Logarithm with specified base: 16 log 2 = 4
or	or	OR, ||	Logical or
and	and	AND, &&	Logical and

Variables

Variable could bea an integer, boolean or double.
Variable names as in Python are just references, they don't refer to specify type.
All possible conversions will be done automatically for example:
true will be cast to 1 or 1.0 if necessary and 0 to false or 0.0

Lists of commands

In many commands you are supposed to add at least one list of commands. These 3 ways of doing this are the same:

if 1>0 forward 100
if 1>0 { forward 100 }
if 1>0 [ forward 100 ]

You can omit brakets when writing only one command. You also can choice between {} and []

Variables name

In order to refer to variable name x you have to add at least one : before variable name. Numbers of : refers to scope. Basically each : refers to one scope starting from : referring to the current scope.
Language supports variables shadowing and using expressions like: ::x could be useful in some situation.
Let examine this code:

let :x 100
repeat 1 {
    let :x 50
    forward ::x
    back :x
}

In this situation turtle will move 100 forward and then 50 back.
It's work a bit different with assign command.

let :x 100
repeat 1 {
    let :x -10
    repeat 1 {
        assign :x 50 // this will affect x from first repeat
        assign ::x 50 // to change global x
        let ::x 25 // will change x from first repeat
        let :x 1
        assign :x 50 // now this will affect x from second repeat
        assign :::x 100 // now this will set global x to initial value
    }
}

The difference is that let counts all scopes but assign counts only those containing selected variable.
So where changing value of variable from outer scope it is better to use assign.
Scopes are counting like in assign also in others commands.

Procedures

There are two commands that are connected with procedures: call and procedure. First is used to call procedure. Second to create it. Example:

procedure square :x {
    repeat 4 {
        forward :x
        left 90
    }
}
call square 100 

Opening application

Download target/LogoTranslator-1.0.jar and exec by command: java -jar LogoTranslator-1.0.jar

This work with java version "17.0.1"

Other option is install Maven project.