SZAFRON, D. AND NG, R. 1990. LexAGen: An interactive incremental scanner generator. Software--- Practice & Experience 20, 5 (May), 459--483.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....the beginning of the previous token if desired. While it is not our belief that character by character analysis is of practical use, the algorithms described here can implement this policy without modification, since it is merely a special case of our more general editing model. Other researchers [Szafron and Ng 1990; Heering et al. 1992] have focused on the problem of incremental generation of batch lexical analyzers, as opposed to incremental lexing. Since language specifications are long lived and infrequently changed relative to the number and frequency of changes made to programs written in those ....

SZAFRON, D. AND NG, R. 1990. LexAGen: An interactive incremental scanner generator. Software--- Practice & Experience 20, 5 (May), 459--483.

....to handle the new 21 kind of token. Alex [14] introduces the if followed by operator to define the right context of a token. Instead of attacking the look ahead problem, this operator actually changes the longest match convention. Alex does not allow look ahead in the general sense. LexAGen [17] solves the look ahead problem in essentially the same way as Alex does. It allows two character look ahead and employs special LookAheadStates to solve the problem. With appropriate modifications to the continuation, action, and output tables, the new scanner discussed in this paper may solve ....

....by hand. However, Waite [18] reports that new scanner generators can produce scanners that are as fast as hand coded scanners. GLA [8] and Mkscan [9] do not support the full set of regular expressions. They aim at handling only those tokens that are used in common programming languages. LexAGen [17] provides a graphic user interface for constructing scanners incrementally. ALADIN [5] ignores the lookahead problem by adopting a multiple match rule, instead of the longest match rule. Incremental lexical analysis in Galaxy [4] did not take the look ahead problem into consideration. Since the ....

Szafron, D. and Ng, R., LexAGen: An interactive incremental scanner generator, Software---Practice and Experience 20(5) pp. 459-483 (May 1990).

....kind of token. In TOOLS [12] backtracking is avoided by adding a new kind of token; it is similar to the error token approach. Alex [9] introduces the if followed by operator. This operator actually changes the longest match convention. Alex does not allow look ahead in the general sense. LexAGen [13] , which is similar to Alex, allows two character look ahead and employs special LookAheadStates to solve the problem. Nawrocki [14] solves a problem similar to that of Alex and LexAGen by checking the left context derived from the LALR grammars of the programming languages. GLA [15] does not ....

....not allowed. Rex [16] which uses a tunnel automaton for efficient scanner generation, does not address the look ahead problem. GLA [15] and Mkscan [17] do not support the full set of regular expressions. They aim at handling only those tokens that are used in common programming languages. LexAGen [13] provides a graphic user interface for constructing scanners incrementally. Incremental generation of lexical analyzers is also discussed in [18] which did not address the lookahead problem. ALADIN [19] ignores the look ahead problem by adopting a multiple match rule, instead of the longest match ....

D. Szafron and R. Ng, LexAGen: An interactive incremental scanner generator, Software---Practice and Experience 20(5) pp. 459-483 (May 1990).

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