Development of a method for checking syntax in a conversational computing system

Three systems in the field of conversational ) computing for small machines have been developed. The main theme has been the exploitation of the full duplex operation of a typewriter to validate the syntax of all expressions and statements entered by the user. A high degree of interaction between the user and his program has been a secordary theme. The first of these systems, called ACTIV-8, was implemented on a D.E.C. PDP-8 computer. This system explored how a computer program might be used to validate the syntax of characters typed by the user. The language implemented by ACTIV-8 was a very limited subset of FORTRAN, and once the concept of echo-checking was developed, its implementation was straightforward. The second system is known as ACL-NOVA and was implemented on a D.G.C. NOVA computer. This svstem was developed by the author and is beinq used on several installations. The last system has the generic name of XB and has been implemented on the D.E.C. PDP-11 computer. Three types of expression have been provided in a language structure designed to demonstrate the svntax and recovery techniques. A concept of a "set of allowable next characters" is developed. A broader view of the validity of expressions is explored. Very flexible neans are available for the user to interact with the system and his program.