Phrase level - for each error entry in table, insert a pointer to a particular error procedure, which assumes the most likely cause, and takes the appropriate action. Assumes error was found in derivation from A, and pretends instead that an A was parsed. Discard states above s, place i on stack. Throw away input symbols until one from follow(A) is reached. Recovery: panic mode - look down stack until state s which has a table entry of Si for one (A) of a set of particular non-terminals.
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#Error handling in compiler design ppt code#
simple to implement - guaranteed to halt - ignores a lot of code phrase level - replace a prefix of current input by string allowing parser to continue. There are a number of different strategies: Error Recovery panic mode - ignore all symbols until a "synchronising" token is found e.g. Poor error recovery causes an avalanche of error messages, whcih are not errors in the source program.
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The parser should: detect all syntactic errors report errors clearly and accurately recover quickly and detect subsequent errors not degrade compiler efficiency The main difficulty in designing the error handling capabilities of a compiler is balancing these competing objectives. Syntax Errors Most errors in programs can be detected in this phase.