Error recovery in parsing relational languages

The ability to report syntactic errors and to recover from them are basic requirements for any programming environment where programs are parsed before execution. Advanced error handling techniques are standard tools when processing textual programs, whereas in the context of visual languages the problem is factually unexplored. We develop an error recovery strategy for the parsing algorithm for atomic relational grammars originally developed by K. Wittenburg (1996). We present a definition of parser defined syntax errors for Wittenburg's parser by analyzing the possible parsing action failures and by showing how an explicit parse trace can be constructed to locate the errors. Then, we present two error recovery techniques, describe how they are integrated to the parses and discuss further directions.