437 research outputs found
Pure 2D picture grammars and languages
A new syntactic model, called pure two-dimensional (2D) context-free grammar (P2DCFG), is introduced based on the notion of pure context-free string grammar. The rectangular picture generative power of this 2D grammar model is investigated. Certain closure properties are obtained. An analogue of this 2D grammar model called pure 2D hexagonal context-free grammar (P2DHCFG) is also considered to generate hexagonal picture arrays on triangular grids
Happy-GLL: modular, reusable and complete top-down parsers for parameterized nonterminals
Parser generators and parser combinator libraries are the most popular tools
for producing parsers. Parser combinators use the host language to provide
reusable components in the form of higher-order functions with parsers as
parameters. Very few parser generators support this kind of reuse through
abstraction and even fewer generate parsers that are as modular and reusable as
the parts of the grammar for which they are produced. This paper presents a
strategy for generating modular, reusable and complete top-down parsers from
syntax descriptions with parameterized nonterminals, based on the FUN-GLL
variant of the GLL algorithm.
The strategy is discussed and demonstrated as a novel back-end for the Happy
parser generator. Happy grammars can contain `parameterized nonterminals' in
which parameters abstract over grammar symbols, granting an abstraction
mechanism to define reusable grammar operators. However, the existing Happy
back-ends do not deliver on the full potential of parameterized nonterminals as
parameterized nonterminals cannot be reused across grammars. Moreover, the
parser generation process may fail to terminate or may result in exponentially
large parsers generated in an exponential amount of time.
The GLL back-end presented in this paper implements parameterized
nonterminals successfully by generating higher-order functions that resemble
parser combinators, inheriting all the advantages of top-down parsing. The
back-end is capable of generating parsers for the full class of context-free
grammars, generates parsers in linear time and generates parsers that find all
derivations of the input string. To our knowledge, the presented GLL back-end
makes Happy the first parser generator that combines all these features.
This paper describes the translation procedure of the GLL back-end and
compares it to the LALR and GLR back-ends of Happy in several experiments.Comment: 15 page
Introducing the Concept of Activation and Blocking of Rules in the General Framework for Regulated Rewriting in Sequential Grammars
We introduce new possibilities to control the application of rules based on
the preceding application of rules which can be de ned for a general model of sequential
grammars and we show some similarities to other control mechanisms as graph-controlled
grammars and matrix grammars with and without applicability checking as well as gram-
mars with random context conditions and ordered grammars. Using both activation and
blocking of rules, in the string and in the multiset case we can show computational com-
pleteness of context-free grammars equipped with the control mechanism of activation
and blocking of rules even when using only two nonterminal symbols
Extraction and integration of data from semi-structured documents into business applications
Cover title.Includes bibliographical references (p. 8).Ph. Bonnet & S. Bressan
On Special forms of Splicing on Arrays and Graphs
Tom Head (1987), in his pioneering work on formal language theory applied to DNA computing, introduced a new operation of splicing on strings, while proposing a model of certain recombination behaviour of DNA molecules under the action of restriction enzymes and ligases. Since then this operation has been studied in great depth giving rise to a number of theoretical results of great interest in formal language theory. Extension of this operation of splicing to higher dimensional structures such as circular words, arrays, trees and graphs have been proposed in the literature. Here we examine the effect of certain specific forms of the splicing operation applied to arrays and graphs
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