SLogo

Description

SLogo is a recreation of Logo - a popular children's coding language. Logo is a user-friendly, interpreted language, designed with a "low floor, high ceiling"; in other words, the designers of Logo intended for the language to allow novice programmers to get started quickly writing programs but also wanted the language to be powerful and extensive for more advanced users.

SLogo uses the MVC paradigm to allow the user to interact with the "turtles" (they can actually become anything you'd like if you upload a new image) on a per expression basis.

Commands

While the command names below are given in all capital letters, SLogo is not case sensitive. Note that any values used as parameters to a command may be the result of calling any of the commands below or a value stored in a variable. Thus all commands return a double value as described below. Also, commands can be formatted over any number of lines, including multiple commands on the same line, but they must be separated by one or more spaces.

Basic Syntax

Token	Syntax	Semantics	Examples
Constant	[0-9].[0-9]	any real valued number note, to avoid potential ambiguity in parsing there should not be a space between the negative sign and the value	50 -1.3
Variable	:[a-z or A-Z]	any word preceded by a colon, : note, if a variable name is used that has not previously been given a value, return a default value (i.e., 0)	:distance :side
Command	[a-z or A-Z]	any word can be a command-name note, all commands return a numeric value note, built-in commands are given below and user-defined commands cannot reuse those names	forward fd
List	[ ]	these brackets enclose a list of zero or more commands or variables note, to make parsing easier, these will always be separated from other tokens by spaces	[ fd 50 rt 90 ]
Comment	#	Ignore any lines that are empty, i.e., only zero or more spaces, and lines that begin with the comment character, "#".	# a comment #fd 50

Turtle Commands (for both a single and multiple turtles)

Name(s)	Description
FORWARD pixels FD pixels	moves turtle forward in its current heading by pixels distance returns the value of pixels
BACK pixels BK pixels	moves turtle backward in its current heading by pixels distance returns the value of pixels
LEFT degrees LT degrees	turns turtle counterclockwise by degrees angle returns the value of degrees
RIGHT degrees RT degrees	turns turtle clockwise by degrees angle returns the value of degrees
SETHEADING degrees SETH degrees	turns turtle to an absolute heading returns number of degrees moved
TOWARDS x y	turns turtle to face the point (x, y), where (0, 0) is the center of the screen returns the number of degrees turtle turned
SETXY x y GOTO x y	moves turtle to an absolute screen position, where (0, 0) is the center of the screen returns the distance turtle moved
PENDOWN PD	puts pen down such that when the turtle moves, it leaves a trail returns 1
PENUP PU	puts pen up such that when the turtle moves, it does not leave a trail returns 0
SHOWTURTLE ST	makes turtle visible returns 1
HIDETURTLE HT	makes turtle invisible returns 0
HOME	moves turtle to the center of the screen (0 0) returns the distance turtle moved
CLEARSCREEN CS	erases turtle's trails and sends it to the home position returns the distance turtle moved

Display Commands

Note, for commands below that receive/return an index number, that index should refer to a list of graphical items (like an image or color) whose items are clearly available in the GUI with their number or order apparent (so the user knows how to refer to them within a command). Also, it would be helpful to populate each list with some initial default choices for the user.

Command	Description
SETBACKGROUND index SETBG index	sets background color of screen to that represented by index returns given index
SETPENCOLOR index SETPC index	sets color of the pen to that represented by index returns given index
SETPENSIZE pixels SETPS pixels	sets size of the pen to be pixels thickness returns given pixels
SETSHAPE index SETSH index	sets shape of turtle to that represented by index returns given index
SETPALETTE index r g b	sets color corresponding at given index to given r g b color values returns given index note, color component values are nonnegative integers less than 256 specifying an amount of red, green, and blue
PENCOLOR PC	returns turtle's current color index
SHAPE SH	returns turtle's current shape index

Multiple Turtle Commands

Command	Description
ID	returns current active turtle's ID number ID values typically start at 1 and increase by 1 with each new turtle created note, there is technically only one "active turtle" at any given time since each command is run once for each active turtle, i.e., this value can always be used to identify the current turtle running the command
TURTLES	returns number of turtles created so far
TELL [ turtle(s) ]	sets turtles that will follow commands hereafter returns last value in turtles list note, if turtle has not previously existed, it is created and placed at the home location note, if more than one turtle is active, commands run return value associated with the last active turtle
ASK [ turtle(s) ] [  command(s) ]	only the turtles given in first list all run commands given in the second list returns result of last command run by the last turtle note, after commands are run, currently active list of turtles returns to that set by the last TELL command (or default active turtle if TELL never given) note, if more than one turtle is active, commands run return value associated with the last active turtle
ASKWITH [ condition ] [  command(s) ]	tell turtles matching given condition to run commands given in the second list returns result of last command run note, after commands are run, currently active list of turtles returns to that set by the last TELL command (or default active turtle if TELL never given) note, if more than one turtle is active, commands run return value associated with the last active turtle

Display Commands

Note, for commands below that receive/return an index number, that index should refer to a list of graphical items (like an image or color) whose items are clearly available in the GUI with their number or order apparent (so the user knows how to refer to them within a command). Also, it would be helpful to populate each list with some initial default choices for the user.

Command	Description
SETBACKGROUND index SETBG index	sets background color of screen to that represented by index returns given index
SETPENCOLOR index SETPC index	sets color of the pen to that represented by index returns given index
SETPENSIZE pixels SETPS pixels	sets size of the pen to be pixels thickness returns given pixels
SETSHAPE index SETSH index	sets shape of turtle to that represented by index returns given index
SETPALETTE index r g b	sets color corresponding at given index to given r g b color values returns given index note, color component values are nonnegative integers less than 256 specifying an amount of red, green, and blue
PENCOLOR PC	returns turtle's current color index
SHAPE SH	returns turtle's current shape index

Multiple Turtle Commands

Command	Description
ID	returns current active turtle's ID number ID values typically start at 1 and increase by 1 with each new turtle created note, there is technically only one "active turtle" at any given time since each command is run once for each active turtle, i.e., this value can always be used to identify the current turtle running the command
TURTLES	returns number of turtles created so far
TELL [ turtle(s) ]	sets turtles that will follow commands hereafter returns last value in turtles list note, if turtle has not previously existed, it is created and placed at the home location note, if more than one turtle is active, commands run return value associated with the last active turtle
ASK [ turtle(s) ] [  command(s) ]	only the turtles given in first list all run commands given in the second list returns result of last command run by the last turtle note, after commands are run, currently active list of turtles returns to that set by the last TELL command (or default active turtle if TELL never given) note, if more than one turtle is active, commands run return value associated with the last active turtle
ASKWITH [ condition ] [  command(s) ]	tell turtles matching given condition to run commands given in the second list returns result of last command run note, after commands are run, currently active list of turtles returns to that set by the last TELL command (or default active turtle if TELL never given) note, if more than one turtle is active, commands run return value associated with the last active turtle

Turtle Queries

Name	Description
XCOR	returns the turtle's X coordinate from the center of the screen
YCOR	returns the turtle's Y coordinate from the center of the screen
HEADING	returns the turtle's heading in degrees
PENDOWN? PENDOWNP	returns 1 if turtle's pen is down, 0 if it is up
SHOWING? SHOWINGP	returns 1 if turtle is showing, 0 if it is hiding

Math Operations

Name	Description
SUM expr1 expr2 + expr1 expr2	returns sum of the values of expr1 and expr2
DIFFERENCE expr1 expr2 - expr1 expr2	returns difference of the values of expr1 and expr2
PRODUCT expr1 expr2 * expr1 expr2	returns product of the values of expr1 and expr2
QUOTIENT expr1 expr2 / expr1 expr2	returns quotient of the values of expr1 and expr2
REMAINDER expr1 expr2 % expr1 expr2	returns remainder on dividing the values of expr1 by expr2
MINUS expr ~ expr	returns negative of the values of expr
RANDOM max	returns random non-negative number strictly less than max
SIN degrees	returns sine of degrees
COS degrees	return cosine of degrees
TAN degrees	returns tangent of degrees
ATAN degrees	returns arctangent of degrees
LOG expr	returns natural log of expr
POW base exponent	returns base raised to the power of the exponent
PI	Reports the number Pi

Boolean Operations

Name	Description
LESS? expr1 expr2 LESSP expr1 expr2	returns 1 if the value of expr1 is strictly less than the value of expr2, otherwise 0
GREATER? expr1 expr2 GREATERP expr1 expr2	returns 1 if the value of expr1 is strictly greater than the value of expr2, otherwise 0
EQUAL? expr1 expr2 EQUALP expr1 expr2	returns 1 if the value of expr1 and the value of expr2 are equal, otherwise 0
NOTEQUAL? expr1 expr2 NOTEQUALP expr1 expr2	returns 1 if the value of expr1 and the value of expr2 are not equal, otherwise 0
AND test1 test2	returns 1 if test1 and test2 are non-zero, otherwise 0
OR test1 test2	returns 1 if test1 or test2 are non-zero, otherwise 0
NOT test	returns 1 if test is 0 and 0 if test is non-zero

Variables, Control Structures, and User-Defined Commands

Name	Description
MAKE variable expr SET variable expr	assigns the value of expr to variable, creating the variable if necessary returns expr
REPEAT expr [ command(s) ]	runs command(s) given in the list the value of expr number of times returns the value of the final command executed (or 0 if no commands are executed) note, the value of the current iteration, starting at 1, is automatically assigned to the variable :repcount so that it can be accessed by the command(s)
DOTIMES [ variable limit ] [ command(s) ]	runs command(s) for each value specified in the range, i.e., from (1 - limit) inclusive returns the value of the final command executed (or 0 if no commands are executed) note, variable is assigned to each succeeding value so that it can be accessed by the command(s)
FOR [ variable start end increment ] [ command(s) ]	runs command(s) for each value specified in the range, i.e., from (start - end), going by increment returns the value of the final command executed (or 0 if no commands are executed) note, variable is assigned to each succeeding value so that it can be accessed by the command(s)
IF expr [ command(s) ]	if expr is not 0, runs the command(s) given in the list returns the value of the final command executed ( (or 0 if no commands are executed)
IFELSE expr [ trueCommand(s) ] [ falseCommand(s) ]	if expr is not 0, runs the trueCommands given in the first list, otherwise runs the falseCommands given in the second list returns the value of the final command executed (or 0 if no commands are executed)
TO commandName [ variable(s) ] [ command(s) ]	assigns command(s) given in the second list to commandName using parameters given in first list as variables when commandName is used later in a program, any given values are assigned to variables that can be accessed when the command list is run and the value of the final command executed is returned (or 0 if no commands are executed) returns 1 if command is successfully defined, otherwise 0

Logistics

Team Members

• Alex Boss
• Hari Rajan
• Belal Taher
• Daniel Rubinstein

Time Taken

Date started: Feb 16

Date finished: Mar 10

Hours spent: 200+