To use any of the computers in the Mathematics Local-Area Network, one must log in, identifying oneself by giving a user name and a password. At the first meeting of the class, you will receive a MathLAN user name and password from the instructor if you did not already have one.
When a MathLAN workstation is not in use, it displays a login screen, with a space (initially labelled `Login') into which one can type one's user name and, later, one's password. If the workstation's monitor is dark, press the Shift key or move the mouse to bring up the login screen.
Moving the mouse around on its pad causes a mouse-controlled pointer to move around in a corresponding way on the screen. Use the mouse to move this pointer into the center of the screen, then type in your user name, in lower-case letters, and press the <Enter> key. The label changes to `Password'. Type your password into the space provided and press <Enter>. (Because no one else should see your password, it is not displayed on screen as you type it in.)
At this point, a computer program that is running on the workstation consults a table of valid user names and passwords. If it does not find the particular combination that you have supplied, it reports that the attempt to log in was unsuccessful (``Authentication failed''). Wait until the `Login' label reappears and then try again.
When the login program has verified your user name and password, it activates a user interface, a program through which one manages various programs and resources that the workstation can access. Our user interface is called GNOME. It takes a few seconds to prepare this interface; during this short period of preparation, the workstation displays a transition screen that reports the completion of each step in the process.
When GNOME takes over, you see at the bottom of the screen a front panel decorated with a variety of icons. You can use most of these icons to activate computer programs. If one places the mouse pointer on top of one of the icons and clicks on the leftmost of the three buttons on the mouse (pressing and releasing it immediately), the program represented by the icon starts to run.
The programs that you start in this way display their output in windows -- rectangles drawn onto the screen, superimposed on the colored background. Each window is enclosed in a frame drawn in one of two contrasting colors, depending on whether or not the window is active: at any given moment, the active window is the one to which anything the user types is directed. A window becomes active when you move the pointer to some exposed point inside the boundary of its frame.
If you want to put a window aside for the moment, with the possibility of returning to it later, look closely at the upper right-hand corner of the window, where the frame contains a small square with a horizontal line, like an underscore, in it. If you move the pointer into that square and click on the left mouse button, you iconify the window, closing it up into a small rectangle on the front panel. An iconified window can be restored by moving the pointer onto its small rectangle and clicking the left mouse button.
When you are done using a workstation, you must log out in order to allow other people to use it. To log out, move the pointer onto the moon-on-monitor icon at the right end of the front panel and click the left mouse button. A confirmation box pops up, asking you to verify that you're ready to log out; move the pointer onto the word OK near the bottom of this box and click the left mouse button. GNOME vanishes, and after a few seconds the login screen reappears. This confirms that you're really logged out.
It is not necessary to turn off the workstation when you are finished. MathLAN workstations can and usually do operate continuously; turning them off and on may actually shorten their life expectancy.
Once you're logged in, it would be a good idea to change your password to something more memorable (but still difficult for others to guess -- think of something arbitrary but vivid). The program that changes passwords is not represented by any icon on the front panel; to run it, you must invoke it by name. The computer program that reads and responds to such invocations is called the shell, and your interactions with the shell takes place in a window generated by a program called a terminal emulator.
Fortunately, there is an icon that starts the terminal emulator -- it's the footprint-on-monitor icon near the left end of the front panel. Move the mouse pointer onto this icon and click the left mouse button. Shortly a window appears, displaying the shell prompt -- the name of the workstation on which the shell is running, followed by a dollar sign. This prompt indicates that the shell is ready to receive instructions.
You type in such instructions using the keyboard. Move the mouse pointer into the terminal emulator window to make it active. Notice that the window frame changes color when the pointer crosses it, indicating that the window has become active.
To shut down the terminal emulator, press <Ctrl/D> -- that is, hold down either of the keys marked <Ctrl>, just below the <Shift> keys, and simultaneously press the <D> key. (On our workstations' keyboards, the keys marked <Ctrl> (``control'') and <Alt> (``alt'' or ``meta'') are somewhat like <Shift> keys, in the sense that they modify the effect of other keys that are pressed simultaneously.) The shell program interprets <Ctrl/D> as a signal that you have no more instructions for it and halts, and the terminal emulator closes the window automatically once the shell stops running.
It is a good idea to change the password associated with your account shortly after you receive it and every few months thereafter. The program that one uses to change one's password is also invoked by its name, password.
Open a terminal emulator, move the pointer into it, and type the word password. The password program prompts you once for your old password -- the one you logged in with -- and twice for your new password. If you give your old password correctly and the two copies of your new password match, the program substitutes the new password for the old one in the table that the login program consults. The old password is discarded and will not be recognized in subsequent logins. (If the attempt to change the password fails for any reason, however, the old password is retained.)
After a successful attempt to change your password, the terminal emulator looks like this:
After running the password program, the shell takes over again and issues another prompt. You can invoke as many programs as you like from the shell, one after another, before pressing <Ctrl/D> to leave the shell.
Many of the handouts and other materials for this course will be distributed over the World Wide Web rather than in paper copies. You can display World Wide Web documents in a window on a MathLAN workstation by invoking the Mozilla browser, a computer program designed specifically to display such documents. (Actually, you can read the handouts for this course on any computer that has a connection to the Internet, and use any browser to display them. Mozilla is simply one of the browsers that is supported on MathLAN. In particular, Netscape Navigator is also available, in case any of you would prefer to use it.)
To start Mozilla, move the pointer onto the red lizard-head icon on the front panel and click the left mouse button. (Some returning students may have the ``walking N'' icon that usually symbolizes Netscape Navigator instead; clicking on it may bring up either Netscape Navigator or Mozilla, depending on how your account is configured.)
Initially, Mozilla displays a World Wide Web document entitled ``The origin,'' which is an entry point to the Mathematics and Computer Science Department's web site. Near the top of this document, under the heading ``Course front doors,'' you'll see the underlined listing ``CSC 151: Fundamentals of computer science I (Mr. Stone).'' Move the mouse pointer onto this listing and click the left mouse button. ``The origin'' is replaced with the document entitled ``Fundamentals of computer science I,'' which currently matches the paper handout that you received at the beginning of class. This is the course's front-door page. Its contents will change from time to time during the semester. It is convenient to start from this page whenever you're looking for a World Wide Web document related to the course.
Most users of the World Wide Web load most of the documents they examine in just this way -- by clicking on an underlined phrase in the currently displayed document that links to another document of interest. You can follow links in this way indefinitely.
At the top of the window, just below the frame, is a menu bar, providing ways of activating various operations that Mozilla can perform. Eventually you may want to explore a number of these, but for the moment let's just look at one that you're certain to need: the operation of shutting down the program.
Move the mouse pointer onto the word File at the left end of the menu bar, and click the left mouse button. A small menu appears:
Move the mouse pointer onto the word Quit at the bottom of this menu and click the left mouse button. The Mozilla window disappears.
Mozilla maintains a list of documents that you have previously loaded, so that if you decide you want to look at one of them again, you can back up to it. Clicking on the word Back, at the left end of one of the bars near the top of the Mozilla window, re-loads the document from which you reached the one currently displayed. If you move the mouse pointer onto the tiny black upside-down triangle next to the word Back and click the left mouse button, Mozilla displays a menu of the titles of recoverable documents, from which you can select the one you want.
After having moved back in this way, you can advance through the same list again by clicking on the adjacent word Forward.
Mozilla can display any document on the World Wide Web. One way to refer to such a document is to give its Uniform Resource Locator, or URL, which is a kind of address by which Mozilla locates and requests the document. For example, the URL for this very document, the one you're now reading, is
http://www.cs.grinnell.edu/~stone/courses/scheme/getting-started.xhtml
To direct Mozilla to load a document for which you know the URL, bring up the File menu again and select the Open Web Location... operation. A dialogue box pops up. Move the mouse pointer into the long rectangle in the center of this box, click with the left mouse button, type the URL into the rectangle, and press the <Enter> key at the end. The dialogue box disappears and Mozilla loads the requested document.
Because URLs are notoriously hard to remember and to type accurately, Mozilla allows you to place a bookmark on any interesting or important document that you reach. To place a bookmark on the document currently displayed, move the mouse pointer onto the word Bookmarks just above the main display window, press and hold the left mouse button to bring up the corresponding menu, and select the Add Bookmark operation. You can subsequently return to that document by bringing up the Bookmarks menu again and selecting from it the title of the document.
For instance, I recommend that you bookmark the front-door page for this course, so that you can return to it easily, no matter what document is currently displayed. Load it into the Mozilla window (perhaps by using the Back operation) and then use Add Bookmark.
Many of the fundamental ideas of computer science are best learned by reading, writing, and executing small computer programs that illustrate them. One of our most important tools, therefore, is a computer program designed specifically to make it easier to read, write, and execute other computer programs: a programming environment named DrScheme.
To start DrScheme, move the pointer onto the red, white, and blue lambda-in-a circle icon on the front panel and click the left mouse button. It takes a few seconds for DrScheme to start up completely.
DrScheme can deal with computer programs written in any of four dialects of the Scheme programming language. In order to be consistent with our course materials, we're going to proceed directly to the ``Graphical'' option, which is quite close to the national standard. This version is consistent with our course materials.
When you start DrScheme for the first time, it may ask you which dialect you want to use. In this case, you should look for the little triangle next to "PLT". Click on this option, if needed, so that the triangle points down. Three options should appear below "PLT". Click on the second of these options, "Graphical (MrEd, includes MzScheme)". Move the mouse pointer onto the word OK and click the left mouse button. Now proceed with Dr. Scheme to get the regular interface.
If DrScheme does not ask you about the appropriate dialect, it may expect you to use Beginning Student Scheme, which is a kind of training-wheels dialect that enables DrScheme to catch and diagnose some common mistakes of novice programmers. As noted above, however, we're going to proceed directly to ``Graphical,'' which is more nearly standard. To inform DrScheme of this decision, we'll need an operation accessed through the menu bar. Move the mouse pointer onto the word Language on the menu bar and click the left mouse button to bring up the Language menu. Move the mouse pointer onto the phrase Choose Language and click the left mouse button again to select that operation. Another window appears:
Click on the little triangle next to "PLT" so that it is now pointed down. Three options should appear below "PLT". Click on the second of these new options, "Graphical (MrEd, includes MzScheme)". Move the mouse pointer onto the word OK and click the left mouse button. The extra window disappears, leaving the DrScheme window. Next, move the mouse pointer onto the word Execute (next to a green arrow, just below the menu bar) and press the left mouse button. DrScheme now expects programs in the dialect it calls ``Graphical (MrEd, includes MzScheme).'' This simply means that it will accept all valid Scheme commands, whereas the other language choices are simply subsets of the full set of commands.
Three options should appear below "PLT". Click on the second of these options, "Graphical (MrEd, includes MzScheme)". Move the mouse pointer onto the word OK and click the left mouse button.
Click on the little triangle next to "PLT" so that it is now pointed down. Three options should appear below "PLT". Click on the second of these new options, "Graphical (MrEd, includes MzScheme)". Move the mouse pointer onto the word OK and click the left mouse button. The extra window disappears, leaving the DrScheme window. Next, move the mouse pointer onto the word Execute (next to a green arrow, just below the menu bar) and press the left mouse button. DrScheme now expects programs in the dialect it calls ``Graphical (MrEd, includes MzScheme).'' This simply means that it will accept all valid Scheme commands, whereas the other language choices are simply subsets of the full set of commands.
DrScheme retains the information that you prefer to use the full set of Scheme commands, so that when you log in again tomorrow and start DrScheme again, it will automatically expect programs in that dialect. You won't need to use the Choose Language operation again unless you decide that you'd like to experiment with Beginning Student Scheme or some other dialect.
When DrScheme comes up, you'll see a new window, with two white rectangular text areas against a dark gray background:
At the top of the window, just below the frame, is a menu bar, providing ways of activating various operations that DrScheme can perform. Move the pointer onto the word File at the left end of the menu bar and click the left mouse button to bring up a menu. Move the mouse pointer onto the word Quit at the bottom of this menu and click the left mouse button. DrScheme responds by popping up a confirmation box of its own, the purpose of which is to make sure that you don't shut down DrScheme by mistake:
Move the mouse pointer onto the word Quit in the confirmation box and click the left mouse button. Both the confirmation box and the main DrScheme window disappear.
This document is available on the World Wide Web as
http://www.cs.grinnell.edu/~walker/courses/151.sp04/readings/getting-started.xhtml
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created December 29, 1996 and
revised August 26, 2002 by
John David Stone
(stone@cs.grinnell.edu)
and
Ben Gum
(gum@cs.grinnell.edu) last revised January 19, 2004 by Henry M. Walker at walker@cs.grinnell.edu. |
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| For more information, please contact Henry M. Walker at walker@cs.grinnell.edu. |