Efficient computation of the locally least-cost insertion string for the LR error repair

The locally least-cost error repair scheme, originally presented by Fischer et al. (1979, 1980), is an error repair scheme that permits the construction of a table-driven or algorithmic error repairing parser with the insertion and deletion cost of the terminal symbols given by the compiler designers. Here, the explicit formalisms and efficient algorithms for the LR-based locally least-cost insertion strings are presented. The formula derived is based on the idea that the string to be inserted is the least-cost terminal string that can be derived from the expected vocabulary string or the left context. In the algorithm presented, the storage or time required for computing and storing the closure graph for every state can be reduced to computing and storing the L-relation, which is dependent exclusively on nonterminals.