Pen and Color Commands

Command	Shorthand	Description
PenUp () ;	PU	Move the turtle's pen up (no longer draws)
PenDown () ;	PD	Put the turtle's pen down (will draw or erase as set)
SetPenSize ( Number ) ;		Set the width of the line the turtle's pen will draw
SetPenColor ( List ) ;		Takes a list consisting of three numbers and sets the red, blue and green values for the color of the pen to those values (numbers should be between 0 and 255)

Moving and Turning Commands

Command	Shorthand	Description
Forward ( Number) ;	FD	Move the turtle in the current direction the number of pixels
Backward ( Number) ;	BK	Move the turtle in the opposite direction it is facing the indicated number of pixels
LeftTurn ( Number) ;	LT	Turn the turtle left the indicated number of degrees
RightTurn ( Number) ;	RT	Turn the turtle right the indicated number of degrees

Turtle and Position Commands

Command	Shorthand	Description
ShowTurtle () ;		Make sure the turtle appears on the screen
HideTurtle () ;		Remove the turtle from the screen (it is still there, just hidden)
Position () ;		Returns a list of two elements with the X and Y position of the turtle
Heading () ;		Returns a single value, the current heading of the turtle in degrees
SetPosition ( List ) ;		Takes a list of two numbers and sets the X,Y position of the turtle to those values
SetHeading ( Number ) ;		Set the heading of the turtle to the value provided in degrees

Logo Data Structures and Variables

The base types of KLogo are numbers, strings, and boolean values. Number constants consist of an optional sign (+ or -) followed by one or more digits, and an optional period which can be followed by one or more digits followed by an optional e or E with an optional sign followed by one ore more digits. Examples of Number constants include 0, 12, 13.1, -14.23e-02, +1.41e10, etc.

Strings are represented by an opening double quote character (") followed by 0 or more characters and finishing with a double quote. The characters \t and \n refer to the tab and return characters. A " in the string is signified by \" and a backslash is signaled by \.

Boolean constants include True and False.

A list in KLogo consists of a set of 0 elements between square brackets. Each element of a list can itself be a number, a boolean value, or a list. Examples of lists in KLogo would be [] (the empty list), [1 2], [1 [3] 2], etc.

Variable names in KLLogo start with a letter and are followed by one or more letters, digits, underscore or question mark (?) characters. Examples of names include Hello, A_Var, Junk49, etc.

A variable in KLogo is declared as

Number VariableName ;
Bool VariableName ;
String VariableName ;
List VariableName ;

A variable may be set using the Make command. The command has the format: Make VariableName Value ;

Operators

KLogo includes a number of predefined operators that can be applied to values of appropriate type.

In KLogo if Expr1 and Expr2 are numbers, then so are:

Expr1 + Expr2 - applies to numbers, result is the addition Expr1 and Expr2
Expr1 - Expr2 - applies to numbers, result is Expr2 minusExpr1
Expr1 * Expr2 - applies to numbers, result is the product of Expr1 and Expr2
Expr1 / Expr2 - applies to numbers, result is the quotient of Expr1 and Expr2
Expr1 < Expr2 - applies to numbers, result is true if Expr1 is less than Expr2, otherwise false
Expr1 > Expr2 - applies to numbers, result is true if Expr1 is greater than Expr2, otherwise false
Expr1 <= Expr2 - applies to numbers, result is true if Expr1 is less than or equal to Expr2, otherwise false
Expr1 >= Expr2 - applies to numbers, result is true if Expr1 is greater than or equal to Expr2, otherwise false
abs ( Expr1 ) - applies to numbers, returns the absolute value of Expr1
minus ( Expr1 ) - applies to numbers, returns the negation of Expr1
round ( Expr1 ) - applies to numbers, returns the value of Expr1 rounded to the nearest integer number
floor ( Expr1 )- applies to numbers, returns the value of Expr1 rounded down to the nearest integer
ceil ( Expr1 ) - applies to numbers, returns the value of Expr1 rounded up to the nearest integer
cos ( Expr1 ) - applies to numbers, returns the cos of Expr1 where Expr1 is considered to be a value in degrees
sin ( Expr1 ) - applies to numbers, returns the sin of Expr1 where Expr1 is considered to be a value in degrees
tan ( Expr1 ) - applies to numbers, returns the tan of Expr1 where Expr1 is considered to be a value in degrees
arctan ( Expr1 ) - applies to numbers, returns the arctan of Expr1 where Expr1 is considered to be a value in degrees
exp ( Expr1 ) - applies to numbers, returns the exp of Expr1
ln ( Expr1 ) - applies to numbers, returns the ln of Expr1
random ( Expr1 ) - returns a random whole number less than Expr1, if Expr1 is 1.0, it returns a random floating point number from 0 to 1

In KLogo if Expr1 and Expr2 are booleans, then so are:

Expr1 and Expr2 - applies to boolean values, result is true if Expr1 and Expr2 are both true, otherwise false
Expr1 or Expr2 - applies to boolean values, result is true if either of Expr1 or Expr2 are true, otherwise false
not Expr1 - applies to boolean values, result is true if Expr1 is false or false if Expr1 is true

In KLogo if Expr1 and Expr2 are values, then so are:

Expr1 == Expr2 - applies to all values, result is true if Expr1 is equal to Expr2, otherwise false (note, for lists and strings, is true only if these are the same list value)
Expr1 <> Expr2 - applies to all values, result is true if Expr1 is not equal to Expr2, otherwise false (note, see == above for lists and strings)

The following operators can be applied to a value Expr and returns true if the value is of the given type:

Number? ( Expr ) - true if Expr is a number
String? ( Expr ) - true if Expr is a string
Boolean? ( Expr ) - true if Expr is a boolean value
List? ( Expr ) - true if Expr is a list value

Some specific list and string related operators include:

First ( Expr ) - if Expr is a list, returns the first element of the list, if a string, the first character
Rest ( Expr ) - if Expr is a list, returns a new list without the first element, if a string, a string without the first character
Nth ( Expr1 Expr2 ) - returns the Expr1th member of the list Expr2 or the Expr1th character of the string (numbered from 0)
Empty? ( Expr ) - returns true if Expr is an empty list or empty string
Equal? ( Expr1 Expr2 ) - returns true if Expr1 and Expr2 are equivalent lists or strings

Other Basic Control Commands

if Expr { CommandList } - if Expr is true the list of commands is executed

ifelse Expr { IfCommandList } { ElseCommandList } - if Expr is true the list IfCommandList is executed, otherwise ElseCommandList

for { VariableName StartExpr StopExpr [ StepExpr ] } { CommandList } - sets VariableName to the values starting with StartExpr and ending with StopExpr steping the value by an optional StepExpr each time (otherwise the step is 1 or -1 as appropriate), each time through the loop the CommandList is executed with VariableName set to that value

while Expr { CommandList } - while Expr is true the list of commands is executed and the expression then again tested

print ( Expr ) ; - prints out an ascii representation of Expr to the command window

wait ( Expr ) ; - if Expr is a number then it waits 1/60th of a second for each whole value of Expr

read ( Type ) - is an operator that reads a value from the command line and returns a value of the appropriate Type such as Number, Boolean, String or List.

Creating New Commands/Operators

To ReturnType NewCommandName ( Type1 ParamName1 Type2 ParamName2 ...) { CommandList } - declares a new command or operator, the ReturnType is one of Void, Number, Boolean, String or List and the parameter list is a list of 0 or more parameters each with a type (one of Number, Boolean, String or List) and then a parameter name. The CommandList is a series of commands to execute that may also include a return statement, in the case of a Void command it would simply be return; in the other cases it would be return Expr;