In this thesis, an error repair scheme using two operators $\underline{d}$ and $\underline{x}$ is described. The scheme is efficient in both space and time, which is easy to implement, and which is very well suited for use as an automatic error repair techniques in LR(1)-based parsers.
The scheme operates by inserting a terminal string. The insertable string is simply computed by traversing graphs which are constructed automatically from an LALR(1) grammar and a table of terminal symbol insertion costs.
We have implemented the scheme in an LALR(1) parser for PASCAL programming language.