We talked last month about some of Logo interaction with the BBC filing systems. LSL's new extensions help greatly. We have also discussed the Jack of a re-defineable turtle in the 16K Logos. The Logotron sprite board should prove a very interesting and powerful answer.

Logotron have in fact encountered some problems with their SAVE primitive when trying to save to cassette or on Econet Fileserver. Two small procedures are listed as figures one and two which deal with, respectively, saving entire workspace and named procedures or global variables. Thanks to Logotron for this information.

There is certainly an argument in favour of cassette-based systems going for a more comprehensive version of the language held in ROM, thus avoiding the administration of large numbers of Logo files stored serially on cassette.

Both 16K Logos still manage a considerable range of primitives, the built-in procedures of a Logo implementation, well over 100 in each. Logotron decided not to include extended name versions of primitives e.g. READLIST for RL. It is very easy for teachers or parents to define suitable long names, for instance: TO READLIST RL LSL supports longer primitives in line with its general policy of making the language easily accessible to younger users of the language. Both versions contain an adequate number of Coe dealing with arithmetic, COS, SIN, TAN, SQRT (in Logotron) ATAN (in LSL) etc. The all-important addition, subtraction, division and multiplication bring us to a point of policy.

Logotron Logo supports both Infix and Prefix notation, in other words both 3 + 4 and ADD 3 4, both 3 * 4 and PROD 3 4. A prefix primitive like EQUAL? can act as the equivalent of = or as a logical operation, returning a TRUE or FALSE value depending on whether the inputs add up.

LSL version 1.00 insists on the use of Prefix notation and its use extends to primitives like GREATER and LESS, BOTH and EITHER and NOT.

Logotron Logo follows the standard for editors and is very easy to use, the best of all the four available. You can define procedures outside the editor with TO...END but the editor is usually where most of the development work for a program goes on. It's a full screen editor, the cursor keys shooting you around the program. Insert mode is standard, word processor style. The function keys are utilised for more specialised functions, like deleting a line and saving it into a "kill" buffer - a straightforward way of repeating oft used lines. You can scroll around large programs, and centre the text you are working on. And then there is the Find and Replace facility, an invaluable option and one which has found its way into BASIC extensions recently. CTRL-C changes your workspace according to your changes in the editor, Escape aborts without changing definitions.

LSL's editor is non-standard. You cannot define procedures from outside. It is not a full screen editor and has more in common with the way BASIC is edited on the BBC. The procedures are listed and the relevant line copied to the bottom of the screen for editing.

A new version of LSL Logo is now available which overcomes many of the criticisms raised. Among the new features is the ability to use TO and END to define procedure.

Further improvements include a MAKELIST primitive - which enables the programmer to create lists with dynamically evaluated elements (variables). Also included is a SEntence primitive.

LSL have also published a set of ten benchmarks and their results to support claims of superior speed and efficient use of workspace. The comparisons are with nearest rival (on speed) Logotron Logo. The benchmarks vary from simple screen output to the dreaded Fibonacci number series test.

Logotron is proved faster at graphics drawing but more complex recursion is handled better by LSL. LSL also affirm that their Logo takes longer to fill up workspace when asked to do so with a Sieve procedure. It shows especially good performance with a second processor in tow.

Three of the relevant procedures are listed here. LSL will supply a benchmark disc to interested parties. It's quite exciting for a race between turtles, isn't it?

A new LSL utilities disc is also now available. It contains machine code extensions to drive the Valiant and Jessop (serial) turtles and a printer screen dump. There are also commands to package procedures into single files - essential and most welcome.

A maths toolkit include various mathematical functions and the CALC command which allows infix arithmetic (see above). A list processing toolkit includes property lists and an interfacing kit provides PEEK and POKE and "bitwise" logical functions.

Also available is Control Logo which provides simple commands for communicating with hardware such as robots and buffer boards attached through the user port or 1MHz bus.

All the extensions are available for version 1.2 and a free upgrade to 1.2 will be supplied with orders for extensions. You can get in touch with LSL on their hotline, 0454 313 076 or write to LSL, 316A Richmond Road, Twickenham TW1 2PD.

The Logotron sprite board is about to open up the possibilities of Logo and attract more users to the language for access to hardware animation. The board plugs into the 1MHz bus and controls the video output of the micro, thereby freeing 20K of RAM.

The board provides up to 32 hard sprites to be controlled simultaneously or independently, 56 sprite shapes, 16 colours, shade facilities and collision detection.

The attraction of easy animation and arcade game writing may well prove to be an even more popular entrance into Logo than the turtle graphics. The retail price of the sprite board bundled with Logotron Logo is 239.95. Available to educational establishments for 175 plus VAT. The board alone is available to educational users for 130 plus VAT. Information from Logotron, Ryman House, 59 Markham Street, London SW3 4ND. Tel: 01 352 1088.