US 5,802,262 AGranted

Method and apparatus for diagnosing lexical errors

AssigneeSun Microsystems, Inc.

InventorMichael L. Van De Vanter

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Abstract

A method and lexical analyzer for diagnosing lexical errors in a stream of symbols. An error-diagnosing lexical analyzer is constructed by a lexical analyzer generator based on a list of regular expression patterns. The list of regular expression patterns includes patterns which define specific invalid lexeme types as well as specific valid lexeme types. The lexical analyzer generated based on the list of regular expression patterns has a first plurality of states and a second plurality of states. Each state of the first plurality of states represents a specific valid lexeme type and is associated with a label identifying the specific valid lexeme type. Each state of the second plurality of states represents a specific invalid lexeme type and is associated with a label identifying the specific invalid lexeme type. The lexical analyzer reads symbols from a stream of symbols and changes state based on the symbols according to transition rules. When the lexical analyzer reads a terminating character, the lexical analyzer transmits a signal indicating the lexeme type associated with the state of the lexical analyzer at the time the terminating symbol was encountered. The lexeme type indicated in the signal is used to characterize the series of symbols processed prior to encountering the terminating symbol.

Claims19

Dependent claims

A lexical analyzer for diagnosing lexical errors in a stream of symbols, the stream of symbols containing symbols from an alphabet of a given language, the lexical analyzer comprising:

a set of states including a first plurality of states and a second plurality of states;
said set of states including an initial state, each state of said set of states being associated with a lexeme type of a set of lexeme types;
said set of lexeme types including a first plurality of lexeme types and a second plurality of lexeme types, each lexeme type of said first plurality of lexeme types being a valid lexeme type in said given language, said second plurality of lexeme types including all possible invalid lexeme types that can be formed in said stream of symbols in said given language;
wherein each state of said first plurality of states is associated with a corresponding lexeme type of said first plurality of lexeme types, and each state of said second plurality of states is associated with a corresponding lexeme type of said second plurality of lexeme types;
a current state indication mechanism configured to initially establish said initial state as a current state;
a symbol input unit configured to repetitively read symbols from said stream of symbols;
a symbol comparison unit configured to determine if a symbol read from said stream of symbols by said symbol input unit is a terminating symbol;
a state change mechanism configured to move from said current state to a next state of said set of states when said symbol is not a terminating symbol, said current state indication mechanism establishing said next state as said current state;
and
a lexeme type signal generator configured to generate a signal indicative of the lexeme type associated with the current state when said symbol is a terminating symbol.

7 more elements

Dependencies are inferred from the claim text.