TEACH POPCOURSE10 - Using online information

Contents

Online information in Poplog

As we have seen, the Poplog system provides us with access to the POP-11 language. POP-11 is a high-level language a small subset of which has been described in the previous POPCOURSE files. In addition to providing POP-11, Poplog also provides the languages Lisp, Prolog and Standard ML. Thus, the Poplog programmer is confronted with various ways of implementing a particular program.

Remembering all the different commands and conventions for all the different languages is an impossible task. To get around this problem Poplog provides an extensive `online' information facility, i.e., an information service that you can get at via Poplog itself. This covers POP-11, the Poplog system in general, the various languages it supports and a host of other things. The intention is that the facility should be accessed by the Poplog user as and when information is needed. It is certainly not intended that the user should read all the information in one go. To make effective use of the information sources you need to develop certain skills. This file teaches those skills and also introduces some of the basic concepts around which the information is organized.

The four basic types of file: HELP, TEACH, REF and DOC

All information in Poplog is presented in files that you read using the Poplog editor (Ved). There are four basic types of file. There are `HELP' files. These typically provide fairly brief information relating to a concrete feature or aspect of Poplog or one of its programming languages. Then there are `TEACH' files. (The POPCOURSE series of files---of which this is one---are all TEACH files.) TEACH files aim to provide a tutorial-style introduction to a relatively abstract topic. In addition to TEACH and HELP files there are also REF and DOC files. These are like reference manuals. REF files are oriented towards the online user. DOC files are primarily intended to be printed out. For our purposes, it is the HELP and TEACH files that are of most interest since they contain the sort of information likely to be of relevance to a novice Poplog user.

All categories of information can be accessed by giving the name of the relevant category as a command. Thus to access a HELP file you give the command `help' followed by the name of the file you want to look at. To access a TEACH file you give the command `teach' followed by the relevant name. And so on. Poplog has a mechanism for creating HELP files on the fly for any word in any of the languages it supports. Thus, you can give the `help' command with the name of any POP-11 command and get some information.

WARNING: When reading HELP files and TEACH files it is important to remember that Poplog has been under development at Sussex and elsewhere for over ten years. Many people have made contributions to the teaching environment (i.e., the collection of TEACH files). Some of these are now out of date or inconsistent in some way. However, they still may be of use as a source of information. It is thus very important to be aware of this problem and not to be dumbfounded by inconsistent, incorrect or out of date information.

Getting started

For each category of file there is an `index' file that lists all the files in the category. You can look at this file by giving an `index' command; e.g. `help index' or `teach index'. If you find the number of files in the index overwhelming you can look at an overview file by giving a `files' command like `help helpfiles' or `teach teachfiles'.

Information files may contain cross-references to other files. By convention, a cross-reference to some particular file is written in upper-case and preceded with either its category (HELP, TEACH, REF or DOC) or an asterisk, or both. A typical example of a cross-reference would be

HELP * STRINGS
though you might also see

HELP STRINGS
and

* STRINGS
Remember that to access this file you give the command `help strings'. You do not include the asterisk in the command.

When you see a cross-reference you may want to follow it up. An easy way to do this involves placing the cursor just before the relevant file-name and hitting the GETSYSFILE key (this is `ESC h' on most keyboards). This key should take you into the relevant file. You can jump to the next (previous) cross-reference by hitting the NEXTHELP (PREVIOUSHELP) key, if your keyboard has one.

The catch-22 of the information system

The catch-22 of online information systems is that to find out something about a particular topic you have to already know something about that topic, namely what its information file is called. If you do not know this then you cannot construct a command to call up the information file.

Poplog provides a command that can sometimes get you out of this dilemma. This is called `helpfor'. When you use this, you include an argument which is just the name of the topic or issue that you are interested in. The command then scans through the documentation for all file-names that have the relevant topic as a substring. Once this list has been compiled, the command takes you into a file that lists explicit cross-references to the relevant files. Thus if you give the command `helpfor strings' you will end up in a files that contains at least the following cross-references.

HELP POP_LONGSTRINGS
HELP STRINGS
REF * STRINGS
To get a sensible response out of `helpfor' you may have to execute it several times. A sensible strategy is to try it out with increasingly short substrings of the topic you are interested in. For example, imagine you want to get some information on the `matcher'. The first command you try is `helpfor matcher'. This produces no information whatsoever. Next you might try `helpfor match'. This produces a list of several files. If you get nowhere with substrings of a particular label try to think of an alternative label for the topic you are interested in.

Getting help on Ved commands

Poplog contains online help for all built-in `words' (procedure names, variables etc.) If you give a command like

help *
you will be taken into the relevant place in a file that deals with the multiplication operator.

If you want help on a Ved command you should remember to append ved_ to the front of the command, since this gives the name of the procedure that actually implements the command. Thus if you want help on the `smr' command you should give the command `help ved_smr'.

Using `indexify' in conjunction with `g'

If you find yourself working in a file that has no index, you can use the command `indexify' to construct one. Once you have executed `indexify', the `g' command will work as usual.

Searching the sources

Poplog is implemented using a dialect of POP-11. For some purposes it can be helpful to see exactly how a particular built-in procedure or command is implemented. If your Poplog system has the source-files contained within it, you can search for the sourcefile containing the definition of a particular procedure by using the `sourcefile' command. For example, to inspect the definition of `member' you would do `sourcefile member'.

Switching between different files

When using the online information files you may end up with a large number of files open at once. The FILESELECT facility provides an easy way of jumping between files. To use it, you hit the FILESELECT key (or sequence of keys). Poplog then shows a list of filenames with numbers. You then type the number of the file you want and Poplog takes you into the relevant file. See HELP VEDFILESELECT for more information.

Information on recent additions to the Poplog system

Poplog is still under development. For news on the latest additions to the system give the command `help news'.

Literature sources for POP-11

The Poplog online information files are not the only further source of information on POP-11. There are also a number of books that provide useful information. The main reference text for POP-11 is still

Barrett, R., Ramsay, A. and Sloman, A. (1985). POP-11: A
PRACTICAL LANGUAGE FOR ARTIFICIAL INTELLIGENCE PROGRAMMING.
Chichester: Ellis Horwood.


There is now an extensive user guide for Ved (available at Sussex from Berry Harper, 4C2).

McIntyre, D., VED USER GUIDE (2nd Edition).


A more limited and elementary text on POP-11 is

Burton, M. and Shadbolt, N. (1987). POP-11: PROGRAMMING FOR
ARTIFICIAL INTELLIGENCE. Addison-Wesley.


For those with slightly more experience on the computer-science side of things there is

Laventhol, J. (1987). PROGRAMMING IN POP-11. Oxford: Blackwell
Scientific Publications.


A book that provides information on a number of large, POP-11 implementations of AI techniques is

Ramsay, A. and Barrett, R. (1987). AI IN PRACTICE: EXAMPLES IN
POP-11. Chichester: Ellis Horwood.


There is also a little information on POP-11 in

Yazdani, M. and Narayanan, A. (1984). ARTIFICIAL INTELLIGENCE:
HUMAN EFFECTS. Chichester: Ellis Horwood.


An interesting BYTE article that praises the worthiness of POP-11 as a programming language is

Pountain, D. (1988). POP goes the macintosh. BYTE, 285-292.


A text (still forthcoming at the present time) that also presents POP-11 based material is

Thornton, C. and du Boulay, B. (1992). ARTIFICIAL
INTELLIGENCE THROUGH SEARCH. Intellect Press.


Exercises

To gain some familiarity with the online information system, you should complete the following exercises. Copy them into a file of your own and then edit in your answers under the questions. If possible get your tutor or a friend to check your answers.

  1. Which online files in Poplog deal explicitly with `documentation'?

  2. In one of the files dealing with `documentation' there is some information that explains the mechanism for accessing a cross-reference to a particular section of a file. How does this mechanism work?

  3. Which file does the command `help +' put you into?

  4. What is the TEACH file called that deals with `discrimination nets'?

  5. List all the possible ways of loading a file.

  6. Which method of returning values (from procedure calls) is used in the examples in `TEACH TOWER'?

  7. How many cross-references to other files are there in this file?

  8. What is the meaning of `SHOWLIB'?

  9. How many files are there that deal with topics whose names contain the substring `data'.

  10. Describe all the shortcut methods that exist for copying a range of text from one file to another.

  11. How does the documentation describe the difference between the `copylist' procedure and the `copytree' procedure.

  12. What happens if you hit the GETSYSFILE key when the cursor is at the beginning of `HELP' in `HELP FOREACH'? What does this tell you about the behaviour of this key-function?

  13. Which files does `TEACH LMR' assume you have already read?

  14. Some TEACH files have indexes included and some do not. Suggest a plausible explanation for this inconsistency.

  15. Is there a built-in POP-11 command that can be used to find out the current time? What sort of value does this procedure return? What online files contain the most useful information about this type of value?

  16. Identify three files, each of which uses a different convention for describing how to issue a command (i.e., a ved command). Describe the differences between the conventions.

  17. What is `TEACH PARPAR' really all about?

Moving on

If you have completed all the exercises satisfactorily you are now ready to move on to TEACH POPCOURSE11. This deals with advanced POP-11 programming. If you are not interested in POP-11 you might like to skip on to TEACH POPCOURSE13, which gives some pointers to other features of Poplog.

Page created on: Fri Apr 26 09:35:01 BST 2002
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