Nick Evans speaks well of the new Acornsoft implementation

Did you know that greedy primitives are needed to tell turtles? No? Then read on, as these are all Logo expressions.

Logo, the language developed by Seymour Papert and his fellow researchers at the Massachusetts Institute of Technology, has had many emulators - some good, some downright ridiculous. Acornsoft's offering, however, is in another league. It bears as much resemblance to many other packages as the Space Shuttle does to the bicycle.

This is a full implementation of the language, using the wide and powerful facilities of the BBC Micro to the full. Papert's vision was of a world where every child would have a powerful micro from the age of about four and, through its use, would develop an understanding of those concerpts which are often taught slowly and poorly by conventional means. This software makes a positive contribution to that ideal.

The first indication of serious intent on Acornsoft's part is that this package consists of two ROMs, a disc and a massive amount of clear documentation. For most people who have made any additions to their micro, the two ROMs will mean an expansion board as well - but if you use Logo in your classroom, the trouble will be well worthwhile.

Every effort has been made to ensure that the user will be able to find his or her way round the language as quickly and easily as possible. Two manuals are supplied - one for those totally new to the idea of computing and Logo, the other for those who are familiar with programming but not with Logo. The user will find that the structures, the keywords (or primitives as they are called - and there are over 200 of them) and the methodology are all expounded in simple terms.

All the usual facilities a Logo programmer would expcet have been built into this package, so the language is quite compatible with other system, and should be able to run a good deal of existing Logo software. However, because of the strides forward made in computing since it was first mooted, much has been added to the original concept - not least the implementation of BBC graphics modes.

Machine code routines and all OSBYTE calls are fully accessible from Logo. The package is compatiable with all the existing floor furtles on the market (Buggy, Variant, Jessop, etc), and it provides hard-copy facilities for a range of printers, allowing a very rapid screen dump to be executed (just under one minute) whenever the machine is in Command Mode.

The 6502 second processor is also compatiable, as are joysticks and other analogue functions, sound and all the range of VDU commands. A character definition program is included on the disc.

Those facilities which are external to Logo and extend its range (e.g. floor-turtles), and termed 'extensions' and are loaded into the workspace either before or during normal program operations. A separate booklet explains their use and operation.

Logo has always been considered by the layman as a language for drawing pretty shapes on the swcreen, exemplified by children sitting around a monitor producing glorified Spirograph patterns. The programs in this package dispel that illusion immediately. Yes, the graphic work is there in all its finery, more detailed still because of the possibility of multiple turtles - you hatch the things - and there is a perspective function, as well as a mirror facility (figure 2) which places two turtles making mirrored images on the screen. However, there is also a good deal of text and number work, often combined with the graphics to provide interesting and stimulating examples.

As well as the usual text facilities it's possible to draw letters on the screen using one of the programs supplied. Their size is determined by input of a number from one to ten. All the normal Logo functions will operate so that the screen may be labelled using this program.

The ability to create a specific Logo 'environment' is central to the principles of the language, and you do this by restricting or extending the facilities offered by the machine - for example, you may wish for single key-presses to represent a particular command, or to 'hide' some of your procedures so that they cannot be analysed by the user. These and other facilities allow you to create an environment which is tailored to the needs of the particular task.

Logo may not be the fastest language around - some of the examples seem very slow. Its most important feature, however, is that it grows in a logical pattern from a starting point easily understood by small children. That is the secret of its success and, with this implementation, a child may now grow up with a version which fully exploits the BBC Micro.

Nick Evans