First Impressions

Here we are. This is the Logo page. To begin with, you have three areas of interest. At the top, the menu bar provides access to Logo’s features. The Graphics panel occupies the top two-thirds of your screen, with the turtle residing in the middle. The Listener occupies the lower part of the screen.

There are many more panels that are not visible initially. You can select the Window menu and then select a panel to make it visible, or you can press a hot key like Ctrl+Alt+E for the Editor panel.

Before You Start

Logo can save a copy of your Logo workspace and the contents of the Editor panel. You should save very often in case your browser crashes, or if you manage to refresh the page by accident. You can change what Logo saves in the Settings dialog.

When you log out, the Web version of Logo asks you if you’d like to keep your Logo data for the next time you log on. If you are a student working in a classroom, it is a good idea to have Logo forget about your personal Logo data unless you want someone else to pick up your work where you left off.

You can also use the RESTART command to erase all saved Logo data.

Configure your Screen Estate

➽ Please note that you cannot drag or resize panels on handheld devices like tablets or smartphones.

Logo’s panels are extremely configurable, which lets you arrange all of these panels to your liking. You can drag panels around, resize them, and rearrange them completely. When you drag a panel, its position and size snaps to a 20×20 grid to help you with the alignment of the panels.

Each panel has three buttons in the upper right corner:

Click this button to shrink the panel to its mere title bar. Click it again to restore the panel.
Click this button to have the panel occupy the entire screen. Click it again to restore the panel.
Click this button to hide the panel. Use the Window menu to show it again.

This is an example where the Listener is at the top, and the Graphics and Toolbox panels at the bottom:

You can save and restore your layout using the Window menu. If you messed up, you can also reload the original Logo panel layout.

Of course, you can also program the panel positions and sizes from Logo if you want your program to arrange the panels. If you save your workspace, the panel layout is saved along with your workspace contents.

Each Logo panel has its own name. This name is available to Logo as a property list. To list the Listener panel properties, for example, you can use the command PLIST “LISTENER.

Let’s talk about the panels one by one.

This is not a real panel, because its position is fixed at the top. You can close the icon toolbar if you need the additional screen real estate. To show the icon toolbar again, use the Window menu.

The Listener

Entering Instructions

The Listener panel is where you type commands or instructions for Logo to do. Often the results will affect the Graphics panel, but sometimes you’ll see a response in the Listener.

Canyoutellwhatthissays? Can you tell what this says? Putting a space between the words of a sentence makes a big difference. The same is true for Logo. When you enter instructions into the Listener panel, make sure you put a space between the words. Press the Enter key to tell Logo to run the instruction.

Make sure the Listener panel is the currently active panel (the one with the highlighted title bar). To make the Listener panel current, just click in it with the mouse, but watch where the vertical insertion bar (or cursor) appears because that’s where your typing will be entered.

The illustration shows some examples that you should try yourself. You can use capital letters if you want; that’s what Logo uses for output but it’s not fussy about your input. Watch carefully as you type the letters and you will see how the colors change. This is called syntax highlighting and it’s much more than just colorful. It can help you avoid errors.

The quotation mark inserted before the word “hello” for example, tells Logo to use the word as is and not to attempt to use it as a command. If you really want to enter lower-case words (in case you want Logo to print them in the same case that you entered them), use vertical bars around the words. You can also use backticks, which automatically also quote the word. (The backtick character is on the same key as the tilde, just below the Esc key.)

Many of the Logo commands have an abbreviation that means the same thing. The PR in the second example is short for PRINT. This saves typing time, but you’ll always know what PRINT means.

To Err is Human

Everybody makes mistakes. It’s going to happen. Even with the syntax highlighting and trying to be very careful, you’re going to press Enter before you see that typo. Don’t worry about it. Logo will quietly let you know there is a problem and then you can fix it easily. In this example, since I forgot to use the quotation mark before the word “hello”, Logo tried to find the HELLO command to print whatever the command outputs instead of just printing “HELLO”. Since Logo didn’t understand this nonsense, it displayed a message to let me know that HELLO was the problem.

What now?? I don’t want to type the whole line again!

There are a few ways I can correct this mistake. I can move the insertion bar with either the mouse or the arrow keys. Since I’m already typing, I find it easier to use the arrow keys. Getting rid of unwanted characters depends on where the insertion bar is placed. If it’s in front of the characters, then use the Delete key; if it’s after the characters, then use the Backspace key. Once I have added the quote character, all I have to do is press the Enter key to make Logo run the instruction again. I could even just use the mouse to highlight any text and press Enter, and Logo will happily attempt to execute all highlighted text.

Pasting Logo Commands

You can also paste entire procedures into the Listener panel. What you need to do, though, is to tell the Listener what exactly Logo should read when you press the Enter key. Usually, Logo reads the line where your cursor is in and runs that line. If you paste more than one line, though, Logo does not know which line to read. Therefore, you will have to highlight everything that Logo should read before pressing Enter. Use your mouse to click and drag the highlighting until you are satisfied, then press Enter. In the example to the left, the entire procedure (which has been pasted before) is highlighted, and Logo would read and define that procedure once you press Enter.

The clipboard is available to you in the Listener and Editor panels, although the menu lacks the menu items “Cut”, “Copy” and “Paste”. This has technical reasons. After you select a text, right-click the text and select “Cut” or “Copy”. To insert text, right-click the panel at the desired location and select “Paste”.

You can also use the standard keyboard shortcuts on desktop systems:

Ctrl+C or Cmd+C

Copy

Ctrl+X or Cmd+X

Ctrl+V or Cmd+V

Paste

Debugger Buttons

The two buttons in the upper right corner are active when a Logo program is running. The left button pauses the program and enters the debugger, and the right button stops your program altogether. During a pause, the left button turns into a green “Continue” button that lets you continue program execution.

The Graphics Panel

The Graphics panel is your main drawing panel. When your turtle draws, it moves across the panel and leaves a trail much like you would leave a line on a sheet of paper with a pencil.

The Logo “sheet of paper” is actually more like a glass panel. Your background image, color, and pattern go onto the back side of the glass while your turtle drawing goes onto the front side. Turtles, bitmaps and controls rest in front of the glass panel.

This glass panel has a fixed size. It is 2000 pixels wide and 2000 pixels tall, with the turtle coordinates [0 0] in the center. A pixel is like a dot. If you paint the smallest dot on the glass surface, it is a pixel. If you move the turtle 100 units, you actually paint 100 dots or pixels. This means that you can paint 1,000 steps in either vertical or horizontal direction before your painting gets lost.

What you see in the Graphics panel is only a small part of the underlying glass panel. The Graphics panel acts as a viewport (or window) to the glass panel. The Graphics panel can vary greatly in size but does not cause any change to your drawing.

If you had the chance to look at Logo from the side, this is what you might see:

See the thick glass plate? On the back side, you can see a background image, and the turtle has drawn a red square onto the front of the glass. The turtle itself hovers over the glass and the viewport is above all, hiding most of the picture.

Going back to the screen and looking at the whole thing from above, you would see this through your viewport.

The Toolbox

The Toolbox panel contains many resources you can use in your Logo projects such as controls, shapes, backgrounds and colors. The popup list at the top of the Toolbox lets you select any of the panels.

The Toolbox panel is hidden to begin with, Select Window/Toolbox or press Ctrl+Alt+T to make it appear.

For right now, select the Colors panel. To use a color, just drag it from the panel to the Graphics panel or a turtle.

The Colors panel shows the 138 extended colors arranged in groups by shades of intensity (from light to dark). You can see each color’s name by hovering the mouse pointer over a block. The COLORS command displays a list of all 138 color names; type SHOW COLORS in the Listener panel to see the list of color words in numerical order.

If you drop a color on top of a turtle, it sets the turtle’s pen color. If you drop a color onto the Graphics panel, the drop spot is the origin of a FILL command with the dropped color. However, if you press the Ctrl button during the drop, Logo uses the color as the background color, and does not alter the graphics itself.

The color words can be used in SETPC and SETBG. Put a double quotation mark in front of the color word. Try SETBG "ORANGE. If you can’t decide on a color yourself, try SETPC PICK COLORS.

The Toolbox contains a huge number of images. Drag an image, like an animal, to the Graphics panel, and create a new turtle that has the shape of this animal. You can also drop an animal on top of a turtle to change its shape. The “Backgrounds” toolbox contains a number of backgrounds; drop one of them on the Graphics panel to see how it works. The “Tiled Backgrounds” toolbox also contains background images, but these are tiled, meaning that they are stitched together to form a background.

Finally, the “Controls” toolbox contains a number of control elements that you can drag to the Graphics panel. When you drop a control, it is created as a turtle with a few extra properties and procedures to put these controls into life. See the section about controls for details.

Did you know that you can drop toolbox items and files into the Listener or into the Editor? When you drop a file, it drops the item’s complete file name. This can save you a lot of typing when you write a Logo command that works with a file name!

The Files Panel

Before we talk about the Files panel, let us talk a little about folders and files.

You may already be familiar with the folders and files on your disk. There are folders within folders within folders. It may seem a little messy at first, but there is method to all this madness - organization! You’ll find this to be a big help when you need to find a sound to play or a view of the earth from the moon.

Browsers cannot access your computer’s files. This is a security restriction. Imagine a malicious Web page that reads your most important and private data and sends them off to someone with bad ideas about your private data! Therefore, Logo offers several ways to access files and folders apart from your hard drive. The Files Panel is a window into these storage systems. It has a drop-down list of storages at the top where you can select the storage to view. A small Refresh button at the top right lets you refresh the contents of the panel in case someone else has changed any files or folders in a cloud storage.

The chapter Where are my Files? has many more details about the available storage systems.

The Files panel is hidden to begin with, Select Window/Files or press Alt+F to make it appear.

Logo Help

This panel contains the entire online reference for all Logo commands. You can click and browse all commands. Many commands come with sample code, which you can copy and then paste into your Listener input field; press Enter to execute the sample code after pasting. You can also use the HELP command to find a specific command. Just enter HELP “command into the Listener input field and press Enter (substitute “command” with the command that you would like to learn about as, for example, HELP "FD).

The buttons display either the home page, the list of commands, the list of properties, or the previous and next commands that you have entered into the input field. Note that if you click any links in the help page, these links will not change the list of pages that you can view with the two right buttons; they keep only track of the commands that you have entered, or commands that you displayed with the HELP and PHELP commands.

The Help panel is hidden to begin with, Select Window/Help or press F1 to make it appear.

The Logo Editor

The Editor panel is hidden to begin with, Select Window/Editor or press Ctrl+Alt+E to make it appear. This panel is a full-blown Logo editor with syntax highlighting and more. When you click its “Run” button, it loads the entire contents into Logo workspace and executes the code. You can also edit a file (Select File/Load Editor on the Menu), or save the editor contents to disk or a cloud storage.

Blocks

The Blocks panel lets beginners get an easy start with Logo. Please refer to the next chapter for details.

Let us look at the menu bar and its items. Many menu commands have “hot keys” or key combinations attached to them you can press to invoke the menu command. Please note that handheld devices like tables or smartphones do not offer hot keys.

File

The File menu lets you manage files.

Load…: The Load menu has several sub-items. You can load a Logo file or a Zip archive from disk into your workspace. Logo loads and executes a Logo file immediately. It loads Zip archives into the Files panel; then, it collects all .LGO files at the top level and runs them in no particular order. Or you load a file into the editor, you load a workspace or a picture, or you load a Zip archive into the Files panel. See this page for more info.

Save: The Save menu has the same sub-items as the Load menu. You can save the workspace, the editor contents, the Files panel, the environment, or the Graphics panel as a picture. See this page for more info.

Print: Here, you can choose between printing the contents of the Editor panel, the Listener contents, or a screen shot of your Logo window. Note that printing the Editor contents or the Listener does not print any colors; Logo only prints the contents without any extra formatting.

Logout: You can log out by selecting this menu item.

Edit

This menu is only active when the Editor panel is active; it contains a number of editing commands, like Cut, Copy or Paste, or Find and Replace.

Debug

This menu contains a number of debugging commands. It is only available when a program has been paused. See Squash the Bugs! for details.

Tools

The Tools menu collects a number of edit commands, and a few important dialogs.

New Procedure: Opens the Editor panel with an empty procedure template for you to fill in and define. You can also enter the first line of a procedure definition beginning with TO into the Listener panel to edit or define a procedure.

Edit…: The Edit menu items lets you edit all procedures, names etc.

Select Voice… lets you select a voice that Logo uses to speak to you when you use the SAY command.

Shape Editor… launches the shape editor.

Settings…: Opens the Settings dialog, where you can edit your password, or your Dropbox connection, or modify Logo’s global settings.

Apps…: Open the Apps dialog, which displays a list of all available apps.

Publish…: This command lets you publish your workspace as a separate Web application. The chapter ”Become a Publisher” contains more information.

Window

This menu lists all panels, and whether they are visible or not. For each panel, the menu defines a hot key for quick access. It also includes items to manage your panel layout:

Save Layout: Saves your current layout to an internal storage location, where Logo reloads it every time it starts. Please note that students who log on to a classroom cannot save the layout.

Restore Layout: Select this item if you want to restore the last saved layout of your panels.

Select Layout…: Lets you pick one of several predefined layouts.

Help

The Help menu lets you display the Help panel, or it displays information about a Logo app, or Terrapin Logo itself. The command “Help/Hot Keys” lists all hot keys that Logo knows, which can be very helpful.