9.3 RECOVERY FROM SYNTACTIC PHASE ERRORS

9.2 RECOVERY FROM LEXICAL PHASE ERRORS

The lexical analyzer detects an error when it discovers that an input's prefix does not fit the specification of any token class. After detecting an error, the lexical analyzer can invoke an error recovery routine. This can entail a variety of remedial actions.

The simplest possible error recovery is to skip the erroneous characters until the lexical analyzer finds another token. But this is likely to cause the parser to read a deletion error, which can cause severe difficulties in the syntaxanalysis and remaining phases. One way the parser can help the lexical analyzer can improve its ability to recover from errors is to make its list of legitimate tokens (in the current context) available to the error recovery routine. The error-recovery routine can then decide whether a remaining input's prefix matches one of these tokens closely enough to be treated as that token.