655 research outputs found
Generalizing input-driven languages: theoretical and practical benefits
Regular languages (RL) are the simplest family in Chomsky's hierarchy. Thanks
to their simplicity they enjoy various nice algebraic and logic properties that
have been successfully exploited in many application fields. Practically all of
their related problems are decidable, so that they support automatic
verification algorithms. Also, they can be recognized in real-time.
Context-free languages (CFL) are another major family well-suited to
formalize programming, natural, and many other classes of languages; their
increased generative power w.r.t. RL, however, causes the loss of several
closure properties and of the decidability of important problems; furthermore
they need complex parsing algorithms. Thus, various subclasses thereof have
been defined with different goals, spanning from efficient, deterministic
parsing to closure properties, logic characterization and automatic
verification techniques.
Among CFL subclasses, so-called structured ones, i.e., those where the
typical tree-structure is visible in the sentences, exhibit many of the
algebraic and logic properties of RL, whereas deterministic CFL have been
thoroughly exploited in compiler construction and other application fields.
After surveying and comparing the main properties of those various language
families, we go back to operator precedence languages (OPL), an old family
through which R. Floyd pioneered deterministic parsing, and we show that they
offer unexpected properties in two fields so far investigated in totally
independent ways: they enable parsing parallelization in a more effective way
than traditional sequential parsers, and exhibit the same algebraic and logic
properties so far obtained only for less expressive language families
A survey of compiler development aids
A theoretical background was established for the compilation process by dividing it into five phases and explaining the concepts and algorithms that underpin each. The five selected phases were lexical analysis, syntax analysis, semantic analysis, optimization, and code generation. Graph theoretical optimization techniques were presented, and approaches to code generation were described for both one-pass and multipass compilation environments. Following the initial tutorial sections, more than 20 tools that were developed to aid in the process of writing compilers were surveyed. Eight of the more recent compiler development aids were selected for special attention - SIMCMP/STAGE2, LANG-PAK, COGENT, XPL, AED, CWIC, LIS, and JOCIT. The impact of compiler development aids were assessed some of their shortcomings and some of the areas of research currently in progress were inspected
A Neural Network Architecture for Syntax Analysis
Artificial neural networks (ANNs), due to their inherent parallelism and potential fault tolerance, offer an attractive paradigm for robust and efficient implementations of syntax analyzers. This paper proposes a modular neural network architecture for syntax analysis on continuous input stream of characters. The components of the proposed architecture include neural network designs for a stack, a lexical analyzer, a grammar parser and a parse tree construction module. The proposed NN stack allows simulation of a stack of large depth, needs no training, and hence is not application-specific. The proposed NN lexical analyzer provides a relatively efficient and high performance alternative to current computer systems for lexical analysis especially in natural language processing applications. The proposed NN parser generates parse trees by parsing strings from widely used subsets of deterministic context-free languages (generated by LR grammars). The estimated performance of the proposed neural network architecture (based on current CMOS VLSI technology) for syntax analysis is compared with that of commonly used approaches to syntax analysis in current computer systems. The results of this performance comparison suggest that the proposed neural network architecture offers an attractive approach for syntax analysis in a wide range of practical applications such as programming language compilation and natural language processing
LR(k) sparse-parsers and their optimisation
PhD ThesisA method of syntactic analysis is developed which . .
is believed to surpass all known competitors in all major
respects.
I
The method is based upon that associated with the
LR(k) grammars but is faster because it bypasses all
reduction steps concerned with 'chain' productions. These
are freely selected productions which are considered
semantically irrelevant and whose right parts consist of
just a single symbol. The parses produced by the method
are 'sparse' in that they contain no references to chain
productions - they are termed 'chain-free' parses.
The CFLR(k) grammars are introduced as the largest
class which can be -Chain-F-ree parsed from -Le-ft to Right while looking ~ symbols ahead of the current point of the
parse. The properties of these grammars are examined in
detail and their relationship to the conventional LR(k)
grammars is explored. Techniques are presented for testing
grammars for the CFLR(k) property and for constructing
chain-free parsers for those grammars possessing the
property. Methods are also presented for. converting
ordinary LR(k) parsers into chain-free parsers.
CFLR(k) parsers are more widely applicable than
their LR(k) counterparts, are faster 'and provide the same
excellent detection of syntactic errors. Unfortunately they
also tend to be rather larger. A 'simple optimization is
presented which completely'overcomes this single disadvantage
without sacrificing any of the advantages of the
method.
These theoretical techniques are adapted to provide
truly practical chain-free parsers based on the conventional
SLR and,LALR parsing methods. Detailed consideration
is given to use of 'default reductions' and related
techniques for achd.evfng compact representations of these
parsers. The resulting chain-free parsers are not only
faster than their ordinary counterparts, but probably
smaller too. We believe their advantages are such that they
should substantially replace other parsing methods currently
used in programming language compilers
A Drop-in Replacement for LR(1) Table-Driven Parsing
This paper presents a construction method for a deterministic one-symbol look-ahead LR parser which allows non-terminals in the parser look-ahead. This effectively relaxes the requirement of parsing the reverse of the right-most derivation of a string/sentence. This is achieved by replacing the deterministic push down automata of LR parsing by a two-stack automata. The class of grammars accepted by the two-stack parser properly contains the LR(k) grammars. Since the modification to the table-driven LR parsing process is relatively minor and mostly impacts the creation of the goto and action tables, a parser modified to adopt the two-stack process should be comparable in size and performance to LR parsers.</p
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