Eberhard Bertsch

Regular Closure of Deterministic Languages

We recall the notion of regular closure of classes of languages. We present two important results. The first result is that all languages which are in the regular closure of the class of deterministic (context-free) languages can be recognized in linear time. This is a nontrivial result, since this closure contains many inherently ambiguous languages. The second result is that the class of deterministic languages is contained in the closure of the class of deterministic languages with the prefix property or, stated in an equivalent way, all LR(k) languages are in the regular closure of the class of LR(0) languages.

Linear-time suffix parsing for deterministic languages

We present a linear-time algorithm to decide for any fixed deterministic context-free language <italic>L</italic> and input string <italic>w</italic> whether <italic>w</italic>is a suffix of some string in <italic>L</italic>. In contrast to a previously published technique, the decision procedure may be extended to produce syntactic structures (parses) without an increase in time complexity. We also show how this algorithm may be applied to pocess incorrect input in linear time.

Size/lookahead tradeoff for LL (k) -grammars

For a family of languages a precise tradeoff relationship between the size of LL(k) grammars and the length k of lookahead is demonstrated.

On failure of the pruning technique in “Error repair in shift-reduce parsers”

A previous article presented a technique to compute the least-cost error repair by incrementally generating configurations that result from inserting and deleting tokens a syntactically incorrect input. An additional mechanism to improve the run-time efficiency of this algorithm by pruning some of the configurations was discussed as well. In this communication we show that the pruning mechanism may lead to suboptimal repairs or may block all repairs. Certain grammatical errors in a common construct of the Java programming language also lead to the above kind of failure.

Some observations on LR-like parsing with delayed reduction

We discuss a bottom-up parsing technique based on delayed reductions, and investigate its capabilities and limitations. Some non-LR(k) grammars, for any k, are handled deterministically by this method. Surprisingly, and counter-intuitively from the viewpoint of LR(k), increase of delay may lead to decrease of determinism. We also present a variant that uses both delay and lookahead.

An observation on suffix redundancy in LL(1) error repair

We give a simple grammatical characterization of the notion of suffix redundancy presented procedurally in a recent article by Fischer and Mauney. It is shown that certain properties of grammars related to suffix redundancy can be decided at parser generation time. Some suggestions concerning efficiency of repair attempts conclude the article.

Fast parallel recognition of LR language suffixes

It is shown that suffix recognition for deterministic context-free languages can be done on a PRAM multi-processor within the upper complexity bounds of the graph reachability problem.

An innovative finite state concept for recognition and parsing of context-free languages

In the full paper in the companion volume, we introduce a new subclass of the context free languages, the meta-deterministic languages, which includes the deterministic languages, but also the languages that result if deterministic languages are combined via regular expressions.

On LR parsing with selective delays

The paper investigates an extension of LR parsing that allows the delay of parsing decisions until a sufficient amount of context has been processed. We provide two characterizations for the resulting class of grammars, one based on grammar transformations, the other on the direct construction of a parser. We also report on experiments with a grammar collection.

Ähnlichkeit von Grammatiken — Ansätze und Erfahrungen

Es wird erortert, unter welchen Umstanden die Ersetzung der Syntax einer Sprache durch eine aquivalente Syntax zu praktisch nutzbaren Ergebnissen fuhren kann. Die betrachteten Verfahren werden insbesondere anhand der Ausdrucks-Syntaxen von PASCAL und MODULA-2 konkretisiert. Unter Ruckgriff auf fruhere theoretische Ergebnisse werden Perspektiven fur den Ausbau der einfachen Ansatze aufgezeigt.