.NHEducational Assumptions and Design..PPFirst, the way to teach people how to do somethingis to have them do it.  Scripts shouldnot contain long pieces of explanation; they shouldinstead frequently ask the student to do some task.So teaching is always by example: the typicalscript fragment shows a small example of sometechnique and then asks theuser to either repeat that example orproduce a variation on it.All are intended to be easy enough that most students will get most questionsright, reinforcing the desired behavior..PPMost lessons fall into one of three types.The simplest presents a lesson and asks for a yes or noanswer to a question.The student is given a chance to experiment before replying.The script checks for the correct reply.Problems of this form are sparingly used..PPThe second type asks for a word or number as an answer.For example a lesson on files might say.IP.IHow many files are there in the current directory?Type ``answer N'', where N is the number of files..R.LPThe student is expected to respond (perhaps after experimenting) with.LP.I	answer 17.R.LPor whatever.Surprisingly often, however, the idea of a substitutable argument(i.e., replacing.IN.Rby17)is difficult for non-programmer students,so the first few such lessons need real care..PPThe third type of lesson is open-ended \(ema task is set for the student,appropriate parts of the input or output are monitored,and the student types .ulreadywhen the task is done.Figure 1 shows a sample dialog that illustrates the last of these, using twolessons about the.I cat(concatenate, i.e., print) command takenfrom early in the script that teachesfile handling.Most.I learnlessons are of this form..KF.TSbox, center;c.T{Figure 1:  Sample dialog from basic files script.sp(Student responsesin italics; `$' is the prompt).nf.spA file can be printed on your terminalby using the "cat" command.  Just say"cat file" where "file" is the file name.For example, there is a file named"food" in this directory.  List itby saying "cat food"; then type "ready".$ \fIcat food\fR  this is the file  named food.$ \fIready\fRGood.  Lesson 3.3a (1)Of course, you can print any file with "cat".In particular, it is common to first use"ls" to find the name of a file and then "cat"to print it.  Note the difference between"ls", which tells you the name of the file,and "cat", which tells you the contents.One file in the current directory is named fora President.  Print the file, then type "ready".$ \fIcat President\fRcat: can't open President$ \fIready\fRSorry, that's not right.  Do you want to try again? \fIyes\fRTry the problem again.$ \fIls\fR\&.ocopyX1roosevelt$ \fIcat roosevelt\fR  this file is named roosevelt  and contains three lines of  text.$ \fIready\fRGood.  Lesson 3.3b (0)The "cat" command can also print several filesat once.  In fact, it is named "cat" as an abbreviationfor "concatenate".....fiT}.TE.sp.KE.PPAfter each correct response the computer congratulatesthe student and indicates the lesson number thathas just been completed, permitting the studentto restart the script after that lesson.If the answer is wrong, the studentis offered a chance to repeat the lesson.The ``speed'' rating of the student (explained insection 5) is given after the lesson number when the lesson is completed successfully; it isprinted only for the aid of script authors checkingout possible errors in the lessons..br.PPIt is assumed that there is no foolproof wayto determine if the student truly ``understands''what he or she is doing;accordingly,the current.Ilearn.Rscriptsonly measure performance, not comprehension.If the student can perform a given task, that is deemed to be ``learning.''.[skinner teaching 1961.].PPThe main point of using the computer is that what the studentdoes is checked for correctness immediately.Unlike many CAI scripts, however, these scripts providefew facilities for dealing with wrong answers.In practice, if most of the answers are not right the script isa failure; the universal solution to student error is to providea new, easier script.Anticipating possible wrong answers is an endless job, and it is reallyeasier as well as better to provide a simpler script..PPAlong with this goes the assumption thatanything can be taught to anybody if it canbe broken into sufficiently small pieces.  Anythingnot absorbed in a single chunk is just subdivided..PPTo avoid boring the faster students,however,an effort is made in the files and editor scripts to providethree tracks of different difficulty.The fastest sequence of lessonsis aimed at roughly the bulk and speed of a typical tutorialmanual and should be adequate for review and forwell-prepared students.The next track is intended for most users and is roughlytwice as long.  Typically, for example, the fast trackmight present an idea and ask for a variation on theexample shown; the normal track will firstask the student to repeat the example that was shownbefore attempting a variation.The third and slowest track, which is oftenthree or four times the length of the fast track,is intended to be adequate for anyone.(The lessons of Figure 1 are from the third track.)The multiple tracks also mean that a student repeating a course is unlikelyto hit the same series of lessons; this makes it profitable for a shakyuser to back up and try again, and many students have done so..PPThe tracks are not completely distinct, however.Depending on the number of correct answers the student has given for thelast few lessons, the program may switch tracks.The driver is actually capable of followingan arbitrary directed graph of lesson sequences, as discussed in section 5.Some more structured arrangement, however, is used in all current scriptsto aid the script writer in organizing the material into lessons.It is sufficiently difficultto write lessonsthat the three-track theoryis not followed very closelyexcept inthe files and editor scripts.Accordingly,in some cases, the fast track is produced merely by skippinglessons from the slower track.In others, there is essentially only one track..PPThe main reason for using the.Ilearn.Rprogram rather thansimply writing the same material as a workbookis not the selection of tracks, butactual hands-on experience.Learning by doingis much more effectivethan pencil and paper exercises..PP.I Learnalso provides a mechanical check on performance.The first version in fact would not letthe student proceed unless itreceived correct answers to the questionsit set and it would not tell a student the right answer.This somewhat Draconian approach has been moderatedin version 2.Lessons are sometimes badly worded or even just plain wrong;in such cases,the student has no recourse.But if a student is simply unable to complete one lesson,that should not prevent access to the rest.Accordingly, the current version of.I learnallows the student to skipa lesson that he cannot pass;a ``no'' answer to the ``Do you want to try again?''question in Figure 1 will pass to the next lesson.It is still true that .I learnwill not tell the student the right answer..PPOf course, there are valid objections to theassumptions above.In particular, some students may object tonot understandingwhat they are doing;and the procedure of smashing everything into small pieces may provokethe retort ``you can't cross a ditch in two jumps.''Since writing CAI scripts is considerablymore tedious than ordinary manuals, however, it is safeto assume that there will always be alternatives to thescripts as a way of learning.In fact, for a reference manual of 3 or 4 pages it wouldnot be surprising to have a tutorial manual of 20 pagesand a (multi-track) script of 100 pages.  Thus the reference manualwill exist long before the scripts.