Input–Output Tools: A Language Facility for Interactive and Real-Time Systems

A conceptual model is discussed which allows the hierarchic definition of high-level input driven objects, called input-output tools, from any set of basic input primitives. An input-output tool is defined as a named object. Its most important elements are the input rule, output rule, internal tool definitions, and a tool body consisting of executable statements. The input rule contains an expression with tool designators as operands and with operators allowing for sequencing, selection, interleaving, and repetition. Input rules are similar in appearance to production rules in grammars. The input expression specifies one or more input sequences, or input patterns, in terms of tool designators. An input parser tries, at run-time, to match (physical) input tokens against active input sequences. If a match between an input token and a tool designator is found, the corresponding tool body is executed, and the output is generated according to specifications in the tool body. The control structures in the input expression allow a variety of input patterns from any number of sources. Tool definitions may occur in-line or be stored in a library. All tools are ultimately encompassed in one tool representing the program.