Abstract

A conservative extension to traditional nondeterministic finite automata is proposed to keep track of the positions in the input string for the last uses of selected transitions, by adding "tags" to transitions. The resulting automata are reminiscent of nondeterministic Mealy machines. Formal semantics of automata with tagged transitions is given. An algorithm is given to convert these augmented automata to corresponding deterministic automata, which can be used to process strings efficiently. Application to regular expressions is discussed, explaining how the algorithms can be used to implement for example substring addressing and a lookahead operator, and some informal comparison to other widely used algorithms is done.

Citations

255	C.: Elements of the Theory of Computation - Lewis, Papadimitriou - 1981
144	Modern Compiler Implementation in Java - Appel - 1998
130	LEX---a lexical analyzer generator - Lesk - 1975
88	String Searching Algorithms - Stephen - 1994
43	Fast text searching for regular expressions or automaton searching on tries - Baeza-Yates, Gonnet - 1996
20	Efficient text searching of regular expressions - Baeza-Yates, Gonnet - 1989
18	flex - The fast lexical analyzer generator - Paxson - 1995
8	Real-time Garbage Collection of a Functional Persistent Heap - Oksanen - 1999
7	Implementing and using finite automata toolkits - Watson - 1996
5	Generation of pattern-matching algorithms by extended regular expressions - Nakata - 1993
5	Regular expressions with semantic rules and their application to data structure directed programs - Nakata, Sassa - 1991
5	A new regular grammar pattern matching algorithm - Watson - 1996