what has a tail and help to give introduction instruction to the computer
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NTRODUCTION
In this lesson, you will write your first computer programs using Logo. After an introduction to the turtle and its environment, you will learn a few commands that the turtle understands. Then it's up to you to instruct the turtle to draw a bunch of stuff.
AN OVERVIEW OF LOGO AND TURTLE GRAPHICS
Logo and "turtle graphics" go back quite a long time (1967). They come from BBN and MIT's Artificial Intelligence Laboratory and the team ofDanny Bobrow, Wally Feurzeig, Seymour Papert, and Cynthia Solomon. Let's read Seymour's own description of it:
... "the turtle." You can think of this as a drawing instrument... Imagine that you are looking at a computer screen. On it you see a small turtle, which moves when you type commands in a language called "turtle talk," leaving a line as it goes. The command "Forward 50" causes the turtle to move straight ahead a certain distance. "Forward 100" will make it move in the same direction twice as far. You soon get the idea that the numbers represent the distance it moves; they can be thought of as turtle steps. Now if you want to make it go in a different direction, you give it a command like "Right 90." It stays in the same place but turns on itself, facing east if it had previously been facing north. With this knowledge you should easily be able to make it draw a box. If that's easy for you, you can think about how to draw a circle, and if that's easy you can try a spiral. Somewhere you will meet your level of difficulty, and when you do I'll give you this piece of advice: Put yourself in the place of the turtle. Imagine yourself moving in the outline of a box or a circle or a spiral or whatever it may be.
Figure 2.1 shows the original turtle from "Mindstorms," Seymour Papert, Basic Books, Inc., 1980.
Figure

jLogo is a version of Logo that is written in the Java programming language. It is sort-of a subset of Berkeley Logo extended to have some traits of Java. Java is just not a good language to start out with. By starting out with jLogo, you will get a good feel for what programming is all about. With this experience, transitioning to Java will not be too hard if this is what you want.
THE GRAPHICS CANVAS - TURTLESPACE
You are going to be learning how to write computer programs which draw things on a digital canvas. This makes a lot of sense because most things that you interact with that contain a computer have a display of some sort or another. Think about it; desktop and notebook computers have flat-panel displays, mobile phones have small displays, tablets - check, new cars have a couple, and now even the Nest Thermostat has a little display... They are everywhere around you.
You are going to be instructing an object, a turtle, to move around on a virtual canvas, drawing as it goes. TG, the program you will use, has an area (a subwindow) called the graphics canvas. Think of it as a two-dimensional world in which the turtle lives.
Here's what the turtle's world looks like. The turtle starts out at the coordinates: 0,0 (the center of its world), heading North. The turtle's world is a bit different from the Cartesian coordinate systemthat you may be familiar with (from your math classes).
Figure 2.2
If you look closely, you'll notice that the origin for angle measurement is different. In turtle graphics, 0 degrees is aligned with the positive Y axis instead of the positive X axis. The other difference is that angle measurement in positive amounts measure clockwise rotation, the opposite direction that you've learned in math classes.
FOUR BASIC COMMANDS
Table 2.1 shows a few Logo commands.
CommandInputsDescriptionExampleFD
FORWARDnumberMoves the turtle forward, in the direction it is facing, by the specified number of turtle steps. One turtle step is equal to onepixel.FD 100BK
BACKnumberMoves the turtle backward, i.e., exactly opposite to the direction that it's facing, by the specified number of turtle steps. One turtle step is equal to one pixel.BACK 150 LT
LEFTnumberTurns the turtle counterclockwise by the specified angle measured by a number of degrees (1/360 of a circle).LEFT 180RT
RIGHTnumberTurns the turtle clockwise by the specified angle, measured in degrees (1/360 of a circle).RT 90Table 2.1
Notice that these commands must include a number, an input. As an example, when you type in a forward command, you must specify some number of turtle steps. This makes sense; if you didn't specify a distance, how would the turtle know when to stop? If you forget to provide the number, you will be reminded, e.g., typing
In this lesson, you will write your first computer programs using Logo. After an introduction to the turtle and its environment, you will learn a few commands that the turtle understands. Then it's up to you to instruct the turtle to draw a bunch of stuff.
AN OVERVIEW OF LOGO AND TURTLE GRAPHICS
Logo and "turtle graphics" go back quite a long time (1967). They come from BBN and MIT's Artificial Intelligence Laboratory and the team ofDanny Bobrow, Wally Feurzeig, Seymour Papert, and Cynthia Solomon. Let's read Seymour's own description of it:
... "the turtle." You can think of this as a drawing instrument... Imagine that you are looking at a computer screen. On it you see a small turtle, which moves when you type commands in a language called "turtle talk," leaving a line as it goes. The command "Forward 50" causes the turtle to move straight ahead a certain distance. "Forward 100" will make it move in the same direction twice as far. You soon get the idea that the numbers represent the distance it moves; they can be thought of as turtle steps. Now if you want to make it go in a different direction, you give it a command like "Right 90." It stays in the same place but turns on itself, facing east if it had previously been facing north. With this knowledge you should easily be able to make it draw a box. If that's easy for you, you can think about how to draw a circle, and if that's easy you can try a spiral. Somewhere you will meet your level of difficulty, and when you do I'll give you this piece of advice: Put yourself in the place of the turtle. Imagine yourself moving in the outline of a box or a circle or a spiral or whatever it may be.
Figure 2.1 shows the original turtle from "Mindstorms," Seymour Papert, Basic Books, Inc., 1980.
Figure

jLogo is a version of Logo that is written in the Java programming language. It is sort-of a subset of Berkeley Logo extended to have some traits of Java. Java is just not a good language to start out with. By starting out with jLogo, you will get a good feel for what programming is all about. With this experience, transitioning to Java will not be too hard if this is what you want.
THE GRAPHICS CANVAS - TURTLESPACE
You are going to be learning how to write computer programs which draw things on a digital canvas. This makes a lot of sense because most things that you interact with that contain a computer have a display of some sort or another. Think about it; desktop and notebook computers have flat-panel displays, mobile phones have small displays, tablets - check, new cars have a couple, and now even the Nest Thermostat has a little display... They are everywhere around you.
You are going to be instructing an object, a turtle, to move around on a virtual canvas, drawing as it goes. TG, the program you will use, has an area (a subwindow) called the graphics canvas. Think of it as a two-dimensional world in which the turtle lives.
Here's what the turtle's world looks like. The turtle starts out at the coordinates: 0,0 (the center of its world), heading North. The turtle's world is a bit different from the Cartesian coordinate systemthat you may be familiar with (from your math classes).
Figure 2.2
If you look closely, you'll notice that the origin for angle measurement is different. In turtle graphics, 0 degrees is aligned with the positive Y axis instead of the positive X axis. The other difference is that angle measurement in positive amounts measure clockwise rotation, the opposite direction that you've learned in math classes.
FOUR BASIC COMMANDS
Table 2.1 shows a few Logo commands.
CommandInputsDescriptionExampleFD
FORWARDnumberMoves the turtle forward, in the direction it is facing, by the specified number of turtle steps. One turtle step is equal to onepixel.FD 100BK
BACKnumberMoves the turtle backward, i.e., exactly opposite to the direction that it's facing, by the specified number of turtle steps. One turtle step is equal to one pixel.BACK 150 LT
LEFTnumberTurns the turtle counterclockwise by the specified angle measured by a number of degrees (1/360 of a circle).LEFT 180RT
RIGHTnumberTurns the turtle clockwise by the specified angle, measured in degrees (1/360 of a circle).RT 90Table 2.1
Notice that these commands must include a number, an input. As an example, when you type in a forward command, you must specify some number of turtle steps. This makes sense; if you didn't specify a distance, how would the turtle know when to stop? If you forget to provide the number, you will be reminded, e.g., typing
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