LEARNING TOOL TURNS TURTLE

Sinclair Logo is the gateway to a new world. Theo Wood emabarks on a voyage of discovery.

Memory: 48K
Price: £39.95

The arrival of the Sinclair version of Logo must be considered as the important event in the year as regards learning software.

Logo is the high level programming language developed at MIT - Massachusetts institute of Technology - by Seymour Papert and his associates. In his book Mindstorms Papert outlined the reasons for the importance of Logo; it provides an introduction to computing for young people in that by controlling the micro-world of the turtle they become actively involved in computing processes. Moreover, mathematical ideas, especially geometry, are made concrete rather than abstract. Logo can also involve those whose background is in the humanities and bring them into contact with a technology that would otherwise seem strange and alien.

Sinclair Logo has been developed by the same team, Logo Computer Systems Inc., who developed the original Apple version as well as the Atari and IBM PC versions and, later this year, the implementation for the BBC micro. The Sinclair version includes a cassette tape with the program and two ring bound manuals.

Logo I covers the use of turtle graphics and Logo II is a programmer's reference manual. There is also a Logo ready reference card. Logo is considered important in that, unlike Basic, it reinforces good programming techniques, encouraging the user to build a program through procedures rather than a spaghetti of GOTOs. That means a program can be structured by breaking each part into its smaller components before incorporating those into the larger structure of the complete program, reflecting the methods used in programming in the commercial world.

Once LOADed, Logo operates in three modes: Logo mode, TO mode and editing mode. In Logo mode any procedure or command such as BK 10, FD 10 - Back, Forward - will be executed on the screen immediately after ENTER has been pressed. That means that at a very early stage you can see the movements resulting from commands immediately and evaluate their success. There are two lines for commands and 22 lines for graphics.

The screen turtle takes the form of a triangle which shows the direction of the heading, although HT - Hide Turtle - will increase the speed at which the turtle can move around. Each procedure has to be started by the use of TO and the title of the procedure and, after this, each entry will be prompted by a > instead of the question mark for the Logo mode. Commands can be ENTERed until the end of the procedure, which is signified by END. The message will then come on the screen - for example, SQUARE defined. It is now possible to use SQUARE as a command in Logo mode.

The EDIT mode is entered by using the message ED "" followed by the name of the procedure to be edited. The editor is powerful; not only can the cursor be moved in all four directions by use of the cursor keys but there are many other useful features such as E MODE - extended mode - 5 which moves the cursor to the beginning of a line and E MODE E which moves the cursor to the end of the text. In that way the editing mode is rather like a word processing package which allows swift movement over a piece of text for correction purposes.

One factor which has importance is the memory space available for utilising Logo features. Logo sits between the addresses 24832 and 65024, its workspace comprising 2293 nodes each of 5 bytes. The command NODES will return the number of free nodes in the workspace. A simple SQUARE procedure - TO SQUARE, REPEAT 4 [FD 30 RT 90], END, requires 120 nodes, which means the workspace can cope with a large number of squares. Any procedures can be SAVEd, for later use and development, to either cassette or microdrive.

Just as the editing mode is relatively simple, so the error messages are easy to understand. 'I don't know how to..." will appear as an error message if the user ENTERs a named procedure in logo mode which has not been defined, and other error messages include 'Not enough inputs to ...' and 'Turtle out of field'.

Logo is a high-level computer language in that its commands are near to language as it is spoken in a shortened form. A list of some of the words used will show how simple the actual vocabulary of Logo is: SETPC - set pen colour followed by a Spectrum colour number; PD - pen down; ST - show turtle. The similarity to spoken language is the main appeal of Logo, as it makes the language more accessible.

That is not, however, the whole story because although the vocabulary is easy the grammar is difficult. It is necessary to observe certain rules in the use of the vocabulary, spaces have to be put in the appropriate places and square brackets have to be used in some circumstances. That means that there still is some learning to be done and attention must be paid to the correct entry of commands; it is no good typing BK30 as the error message will appear: 'I don't know how to BK 30'. There must be a space between BK and 30.

With graphics Logo does, on the whole, satisfy the criteria stipulated by Papert; it is a tool by which you can explore the world of geometry and learn by doing rather than by being told. It provides an entrance into the world of computer programming and inculcates good programming practice.

It is a mistake, however, to think of Logo as merely a learning tool for geometry. Sinclair Logo is the full implementation of the language, providing powerful list processing facilities. A list can be a group of words, other lists or both; for example [apple pear orange banana plum] is a list and a number of commands can be used to manipulate the words contained within the list. PR. - print - ITEM 3 (apple pear orange banana plum] will return orange, and PR LAST will return plum.

Logo has arithmetic functions which can operate in the infix form, where the signs + - * / are placed between the numbers, thus PR 6+789 returns 795. The prefix form also can be used for addition, division and multiplication where the words SUM, DIV or PRODUCT are placed before the two inputs, thus PR SUM 8 9 returns 17.

Logo is likely to be used in control situations without using machine code. Not only can a robotic device be controlled via the commands STARTROBOT and STOPROBOT, which causes the commands FD, BK and so on, to be executed by the device, but there is also the facility to monitor inputs and outputs. SERIALIN will read everything that arrives at the serial port and SERIALOUT will send a byte to the serial port - RS232 interface.

Logo 2, the programmers reference guide, is precisely what its title implies and it would seem that there will be a whole industry of new books based on interpreting and explaining the concepts contained in it. That would be a pity as, ideally, the Logo world should be explored without a phrase book; it is the process of discovery which is important rather than the end product.

Chapter Seven, Conditional expresSions and flow of control, illustrates the nature of the manual. Anyone who has learned some Basic has probably learned the IF command: IF a=5 THEN GOTO. The similar command in Logo is explained in the manual in the following way: IF pred instructio-list 1 instructionlist2. It is necessary to enclose the instruction lists in square brackets. That illustrates that it is misleading to think of Logo as always being more simple than Basic.

One notable feature missing in this version of Logo is the absence of the SPRITE function which both the Atari and the forthcoming BBC version have. That allows the user to piggyback a graphic onto a sprite and then set the speed. As well as having colour and sound the dimension of movement can be easily added, obviously an extra, exciting attraction. Clever programmers will probably use the facIlity to LOAD a machine code routine into the Logo workspace to overcome that lack but it makes the process more complicated. There is no blockfill command either.

Overall, Logo is the package which could become the programming language used throughout the school system and, when the examination boards recognise its use, there will be the extra motivation to buy it. Added to that is the fact that control packages are being developed by the Microelectronics Education Programme and the Open University which indicates that, as well as being the means by which users can explore geometric and mathematical concepts in an interactive way, they will also be able to control and manipulate, electronic devices.

The package costs £39.95 and consequently there is likely to be some price sensitivity to Logo in the home market, especially when considering the bottom line value of the medium - the cassette - on which it is produced.

Logo fully illustrates Paperts insistence that the emphasis should be on user control: forget about zapping answers in response to sums, control what is happening on the screen and at the end of the cable instead. Problem-solving becomes more interesting when the results can be seen immediately and are more spectacular, without the need for complicated Basic commands. Above all, once learned, Logo is a gateway to the complex world of mathematics and computer control.

DESIGNS FOR LIVING

Colin Christmas turns turtle with Sinclair's package.

There are certain people for whom the usual channels of communication, such as a cheerful "Hi. How are you?, Your place or mine?, Leave it out John", and so on, are virtually useless. In this category I put all aliens. Chiefly because I've never met any or at least any who would admit to having come from another world.

Also in this category, anyone from another country who has not learned English, or any other gibberish that I can't understand.

And most mathematicians.

That's my experience for what it's worth. The problem of course is language. Mathematicians seem to have their own and since my only consistent success in that field is to have failed every test and examination they cared to set for me, we never seem to have anything to talk about.

Imagine, then, a cosy meal late into the night and me deep in conversation with a mathematician... She is talking about computers, learning and languages - computer languages. Her enthusiasm for one in particular cannot be ignored. It was called LOGO and all this took place two years ago. She was less of a mathematician, more of a maths teacher.

I hope the relevance of that little anecdote to this article will soon be obvious. Regular readers of ZX Computing will at least be familiar with LOGO through reading excellent articles by Tim Hartnell and the series 'Slogo' by David Nowotnik who has written a BASIC program which gives us quite a powerful and versatile version of LOGO for the 48K Spectrum.

Readers will also (I hope) be well aware of the increasing number of utilities and toolkits being made available to Spectrum users for work in graphics and areas like computer aided design, something of a special interest of mine, as regular readers might have noticed.

GET COMPUTERS iNTO SCHOOL

LOGO is probably best known as a graphics language. Many children today will be familiar with 'buggies' or 'turtles' which many schools bought as part of the package in the great 'Let's get computers into schools' campaign which in fact is still going strong.

These mini robots receive LOGO commands from a computer and move about on sheets of paper on the floor creating designs and shapes. Needless to say, Seymour Papert, the founding father of LOGO, had more than just graphics in mind when designing this language which would 'teach learning'.

He certainly had young children in mind however, and furthermore he had the world of mathematics in mind too. The common denominator would be the computer used as a tool by children. The language would need to be able to develop logical thinking, introduce children to computer programming and at the same time prepare them for future programming and languages other than the cumbersome BASIC.

This was Papert's task. LOGO the result.

It's not the only competitor in the field of languages for education. There's PASCAL, also 'procedure orientated' and Comal which is used educationally in Sweden and Norway.

But it's not my brief to discuss LOGO in detail - there's neither time nor space here - nor to offer comparisons with other languages. Rather, it is to give a considered welcome to Sinclair's LOGO package for the 48K Spectrum.

The package comprises two books, and a software cassette by LCSI/SOLI. The first book, Sinclair LOGO 1, deals exclusively with turtle graphics. The 'turtle' incidentally is not the robot kind but a graphics turtle which appears as a small triangle on the screen.

The graphics screen is known as the TURTLE'S FIELD, and this, apart from the bottom two lines of your TV screen, is your drawing board.

The size of the field can be changed using a very simple command (ALL commands, operations and procedures in LOGO are extremely easy to grasp - almost literally 'childsplay'), this particular command setting the aspect ratio to (XY) which changes the scales on which your images have been drawn.

PRIMITIVES

LOGO understands a number of words called PRIMITIVE PROCEDURES known as PRIMITIVES and many of these have a shorthand form. So that to make the turtle appear on the screen you type SHOWTURTLE or ST (its short form) and to make it disappear you type HIDETURTLE or HT.

The shape of the turtle gives you its POSITION and its HEADING, This is known as the turtle's STATE. Its STATE, BACKGROUND colour, all movement BACK, FORWARD, LEFT, RIGHT, PENCOLOUR (the turtle is imagined as carrying a pen which it draws with, or not because you can instruct the turtle to lift its pen, in which case it does not draw as it moves), the boundaries of its movement, all of these can be changed with abbreviated commands.

Once you have used primitive procedures to draw a square or some other geometrical shape, then LOGO can be taught to understand all of these procedures as one procedure by simply giving it a name.

In this way, by building new procedures you are continually extending LOGO'S vocabulary. And you can master it in minutes.

DOCUMENTATION

The first book goes on to show how you can write programs which can manipulate words and lists, known as OBJECTS in LOGO.

When the software cassette is loaded, the Spectrum is in TEXTSCREEN mode. There are 22 lines available for text.

Every time you use a primitive related to the movement of the turtle, you go into the graphics mode, again with 22 lines for graphics and the two already mentioned which are for your conversation or communication with LOGO. To get back into TEXTSCREEN simply type TS. You cannot of course see the turtle in this mode.

The last part of the first book instructs the user on using VARIABLES, carrying out arithmetic operations, assigning values to variables, exploring the potential of LOGO for producing beautiful designs based on circles polygons and spirals, exploring the capability in LOGO of procedures being able to call or be called by any other procedure including itself (known as recursive procedures), and finally the setting up of a game using LOGO.

I can't truthfully imagine many people finding this first book difficult to use and for that matter, finding LOGO anything but fascinating and challenging to use.

The second book in the package describes itself as "a reference manual for experienced LOGO users, rather than a guide for newcomers." All I can say here is that working through the first book is easy and enjoyable and having done that, by its own definition, the SINCLAIR LOGO package welcomes you to the second book as 'an experienced LOGO user'.

The reference manual is extremely comprehensive and so far has not let me down once. It is set out clearly and is very easy to use for reference. Fourteen chapters and two Appendices take you through first the basic rules for writing and combining procedures, the grammar or the language and from there the using of that grammar to make LOGO understand what you want it to do. Each of the PRIMITIVES is then defined and their use explained in considerable detail. It's this which makes it only suitable for experienced LOGO users, not its degree of difficulty in being understood or used.

GOOD NEWS

Like any new message, the good news of LOGO has been steadily spreading since it was first announced in the sixties. Sinclair have at last now provided Spectrum users with their own 'bible' in the shape of this package. This means more disciples and I think the package will find its first converts amongst those who are in any way 'instructors'.

It is another language, to many of us refreshingly different from BASIC. It is widely recognised that you tend to prefer the language you first learned to program with and so the package will only appeal at first to the most open minded micro users. But now that it is here in this form, I foresee a new wave of programmers and a wider use of LOGO in the vocabulary of children and teachers in particular.

LOGO is something new to Spectrum uses. Its potential for early learning should not be ignored. Once again we have at our fingertips a tool which will become commonplace to future generations or at least act as a stepping stone on the journey toward new horizons for the home computer.

GRAPHICS '85

A comprehensive review of the state of the art by Colin Christmas.

As we see this old year out and welcome the new one in, it's a better time than most to stand back and take stock. Looking back land leaving the prophecies and predictions to others! It must surely be agreed that for Spectrum users with an eye on Graphics it has been a most exciting year. I can't speak for other departments but for me, it has been Christmas every issue.

In this issue I want to do something special take a look at the goodies that have come our way. Our way? Who are We? We are the Graphics Grabbers, Artwork Addicts, Design Doodlers. For us the screen is a window on a world of colour, images, line, shape, pattern, design, texture, light and shade. And like a window it opens out into an exciting new visual world. For business, for profit, for learning for discovering or for pleasure. From the weekend dabbler or doodler to the serious professional, from the games enthusiast to the educational user, from beginner to experienced programmer and right across the age range, you will find Spectrum owners who are hooked on graphics.

It's fairly formidable task - covering the range of Graphics Hardware and Software now available lo Spectrum owners but let's get started.

LIGHTPENS

I've had most success to date, with the package from Dk'tronics. The pen itself is rather like a biro or felt tip pen. It is attached by a wire to a control interface which of course comes with the package. The interface is plugged into the back of the Spectrum. A program on cassette is included.

The glass screen of your monitor is the working area and drawing surface, so some consideration has to be given as to whether this is the way you want to work. Then there are practical aspects such as the distance of your screen from your keyboard, and the fact that you have to work on a perpendicular 'face'. The height of the screen is therefore important if you do not want to suffer from muscle fatigue in your drawing arm.

Lightpens give you a physical contact and interaction with your drawing surface if that is important. Calibrating the pen each time may prove a chore, but after that it's plainsailing - within the limitations of the power of the program. Again it's a good way of getting started or the very basics of graphics, of getting into the picture as it were. Sensibly introduced in the classroom it could be useful aid and introduction for children in an educational context. It is limited though in its potential for advanced or complex screen designs. Graphics Tablets give you similar physical point of con tact with your drawing-surface. This time it is horizontal and again a 'pen' is used. There's a review of the Saga Graphics Pad in this issue. So when you are ready look it up. They certainly take you further than the lightpen. But then you pay a lot more for the facilities they offer.

Now for something almost completely different, the Sinclair LOGO pack. Another excellent starter, but as I have hinted, quite different.

This pack has very obvious educational applications and for very young children. The founding father of the LOGO language intended it as a language for children which would develop logical thinking, introduce young minds to computer programming and have very definite terms of reference for the teaching and development of mathematical concepts. Drawing is achieved by moving a small graphics 'turtle' - a triangle - around the screen. This is done by sending through the computer commands known as Primitive Procedures (mostly single words and abbreviations of those words). Your sense of direction needs to be accurate and formulated mathematically. Once you have established procedures for drawing, say, a square, this group of procedures can be assigned a single word or name which LOGO will then understand as a command to repeat the whole set of procedures.

The emphasis or bias is fundamentally mathematical, arithmetical or geometric. You do not just learn to draw a square, you also learn what makes a square what it is and from there the difference bet ween a square and a rectangle or a parallelogram.

It is a language itself, apart from BASIC. Hence learning to use it is learning to program a computer in another language. The graphic aspect being displayed on the screen is part of the incentive and motivation for progressing with the new language.

Two fairly weighty and comprehensive books or manuals are part of the pack. The first book deals exclusively with Turtle Graphics and is an absorbing and refreshingly different kind of programming experience. The second book acts as a reference manual for Sinclair LOGO, The growth, use and development of LOGO by Spectrum owners, especially in schools will, I think, be affected by the cost factor.

When DREAM SOFTWARE released Computer Aided Designer, my own children had not had their Spectrum for long. They, like me were exploring the full graphics potential of the machine when C.A.D. turned up and kept us enthralled for days. Now, still an old favourite, I would recommend it as another in the 'Starter' category. With very obvious educational values and as a springboard for more ambitious projects later in Design.

The manual is simple and very straightforward - alphabetically leading you through the twenty seven commands available in the program. Some forty custom shaped graphics, UDGs can be designed. By giving precise measurements most geometric shapes can be drawn, filled and so on. It remains impressive after all this time, and the potential for drawing in 3D is considerable.

Similarly, another old favourite, VU-3D from PSION.
This has the added and appeal of enabling the viewer to move around the object in 3D. Graphics and Design, pure and simple. High resolution colour and an incredible understanding of perspectives are real bonuses with this program.

Future designers in the Aircraft or for that matter almost any other industry, may have started young with something like C.A.D. or VU-3D.

I doubt if they would have been able to afford the RD Digital Tracer, from RD Laboratories. This is closer to an instrument than anything else I've come across in graphics and design hardware and software for the Spectrum.

It comes in two versions, the Standard and the Professional. Both are fairly highly technical and sophisticated tools. The Tracer consists of a short fixed arm and pivot from which extends a drawing arm hinged at the centre with another floating pivot which moves across your drawing surface area.

The arm is connected to the computer by a length of cable via an interface plugged into the rear port of the Spectrum. A cardboard template and transparent grid overlay are included for calibration purposes, the tracer is a precision instrument. The software cassette contains five programs. The usual options are offered in the first, plotting single points, construction of basic geometric figures, filling, hatching, change of ink, border, paper colour, adding text, UDGs and so on.

The display image can be moved up, down, and from side to side, scaled up and down, and reversed. Multiple screen images including images at different scales and at different positions can be achieved. By adding other BASIC routines and software, the Tracer's capabilities can be extended into the field of statistical analysis. This immediately puts the Tracer into a specialist Graphics and Display category. Although the Tracer can be used with the ZX81 and 16K Spectrum, its full potential can only really be developed on the 48K and then only by competent programmers. It's a versatile instrument for the specialist.

It's the season of Good will and all that, so why not give a last mention for all whose speciality is Games Designing. It's been around for a while, but standing the test of time in lots of ways. I'm referring of course to the High level User Friendly Realtime Games Designer from Melbourne House. Or as it is more commonly known, HURG.

Still a powerful program and a very good manual. How did they do it in those all time greats like Pacman, Donkey Kong and Space invaders? H.U.R.G. will tell you how.

It's a pretty good list of graphics goodies and that other seasonal expression comes to mind. 'There's something here for everyone.' You have no excuse for not knowing how and from whom in Spectrum Graphics, just how to enjoy the graphics power behind those buttons.

One of the best and least expensive Logo packages available for any machine. It was written for Sinclair by LCSI and provides a full version of Seymour Papert's MIT Logo.

The language was developed for use by children. It is attractive because of its ability to draw simple or complex shapes on the screen using a pen called a Turtle. A robotic device may also be controlled by Logo. The robot, called a floor turtle, will draw the shapes on paper rather than the screen.

Although several companies, notably CP Software, have brought out versions of Logo the Sinclair package is the official version. It is also the fastest and easiest to use.