For decades we have been using Chomsky's generative system of grammars, particularly context-free grammars (CFGs) and regular expressions (REs), to express the syntax of programming languages and protocols. The power of generative grammars to express ambiguity is crucial to their original purpose of modelling natural languages, but this very power makes it unnecessarily difficult both to express and to parse machine-oriented languages using CFGs. Parsing Expression Grammars (PEGs) provide an alternative, recognition-based formal foundation for describing machineoriented syntax, which solves the ambiguity problem by not introducing ambiguity in the first place. Where CFGs express nondeterministic choice between alternatives, PEGs instead use prioritized choice. PEGs address frequently felt expressiveness limitations of CFGs and REs, simplifying syntax definitions and making it unnecessary to separate their lexical and hierarchical components. A linear-time parser can be built for any PEG, avoiding both the complexity and fickleness of LR parsers and the inefficiency of generalized CFG parsing. While PEGs provide a rich set of operators for constructing grammars, they are reducible to two minimal recognition schemas developed around 1970, TS/TDPL and gTS/GTDPL, which are here proven equivalent in effective recognition power.

In this paper we describe the ideas behind the Grammar Workbench (GWB). The GWB is one of a series of tools for the development of AGFLs (affix grammars over a finite lattice) for natural language. Its functions comprise a specialised editor, computation of properties, and special output routines to provide an overview of a grammar. This paper discusses AGFLs, the AGFL project, the functions of the GWB, and some aspects of incremental computation as applied in the GWB.

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Context-Free Grammars (CFGs) are a simple and intuitively appealing formalism for the description of programming languages, but lack the computational power to describe many common language features. Over the past three decades, numerous extensions of the CFG model have been developed. Most of these extensions retain a CFG kernel, and augment it with a distinct facility with greater computational power. However, in all the most powerful CFG extensions, the clarity of the CFG kernel is undermined by the opacity of the more powerful extending facility. An intuitively appealing strategy for CFG extension is grammar adaptability, the principle that declarations in a program effectively modify the context-free grammar of the programming language. An adaptable grammar is equipped with some formal means for modifying its own CFG kernel. Most previous adaptable grammar formalisms have, unfortunately, failed to realize the potential clarity of this concept. In this thesis, a representative samp...

We introduce the bottom-up tree-to-graph transducer, which is very similar to the usual (total deterministic) bottom-up tree transducer except that it translates trees into hypergraphs rather than trees, using hypergraph substitution instead of tree substitution. If every output hypergraph of the transducer is a jungle, i.e., a hypergraph that can be unfolded into a tree, then the tree-to-graph transducer is said to be tree-generating and naturally defines a tree-to-tree translation. We prove that bottom-up tree-to-graph transducers define the same tree-to-tree translations as the previously introduced top-down tree-to-graph transducers. This is in contrast with the well-known incomparability of the usual bottom-up and top-down tree transducers.

Gentle [Schroer 89] is a compiler description language in the tradition of two level grammars [Koster 71] and logic programming [Warren 80]. It provides a common declarative notation for high level description of analysis, transformation, and synthesis. Imperative constructs like global variables and dynamic arrays, needed for efficient compiler construction, are introduced as well. A tool has been implemented to check the wellformedness of Gentle descriptions, and to generate very fast (generation speed 260.000 lines per minute) very efficient compilers (compilation speed nearly 90.000 line per minute on Dec 3100 workstation) . The language and a supporting tool were designed and implemented by F.W. Schroer in 1989. Logic Programming and Compiling Using logic programming as a compiler--writing tool has a long tradition. [Warren 80] shows how Prolog may be used for this purpose and writes: To summarize, Prolog has the following advantages as a compiler--writing tool: 1. Less time an...

Affix Grammars over a Finite Lattice (agfls), a simple form of two-level grammars admitting quite efficient implementations, are proposed as a formalism to express the syntax of natural languages. This paper is concerned with their application in the description of Turkish, a non-Indo-European language with a detailed and complicated morphosyntax. First the concepts and notation of agfls are briefly described, followed by a sketch of a description of the turkish finite verb, including vowel and consonant harmony and the backward effects of suffixes. 1 Introduction Affix Grammars [1] are a formalization of a notion well known to linguists (see e.g. [2]): Context Free grammars augmented with features for expressing agreement between parts of speech. Such grammars have been used extensively in classical Linguistics (albeit in a non-formal form) for more than two thousand years. Although they have been developed and used mostly within the context of compiler construction and formal langua...

In this paper we describe the ideas behind the Grammar Workbench (GWB). The GWB is one of a series of tools for the development of AGFLs (affix grammars over a finite lattice) for natural languages. Its functions comprise a specialised editor, computation of properties, a random generator of sentences, and special functions to provide an overview of a grammar. This paper discusses the functions of the GWB, the grammatical formalism AGFLs, and the AGFL project. We also discuss the relationship between the complete development environment for AGFLs and other development environments, both for other grammatical formalisms and for computer programs. 1 Introduction Formal grammars for natural languages tend to become unmanageable as they get larger. Similar problems occur in the development of large computer programs. To overcome these problems with large programs, a number of techniques have been invented in the field of software engineering to ffl structure programs so as to permit deco...

The framework of the research is the automatic syntactic and semantic analysis of natural language data. A hypothesis about the linguistic structure of a natural language is drafted according to the conditions and conventions of the AGFL 1 formalism and consequently tested at raw ( = untagged) authentic data of the language variety involved to obtain analyzed data and a verified theory. The AGFL formalism is a two-level context-free affix grammar for which a compiler has been made to automatically translate a set of rules into a parser. This formalism, developed for the definition of programming languages, proved to be adequate enough to describe natural languages such as Dutch, English, Hungarian, Spanish as well as Modern Standard Arabic (MSA). We are looking for an answer to the question: How to get good control over the information flow in a linguistic communication system and how to formalize it? In this paper we discuss an improvement in the description of the structure of the noun phrase (NP) and the verb phrase (VP) in MSA as a short introduction to its representation in terms of the AGFL formalism.

There are several ways to create an exact recognizer for the language defined by a context free grammar. The recursive backup technique, proposed by [Kos75], is capable of handling (locally) ambiguous grammars. Due to its structure, it is not limited to context free grammars, but applicable for affix grammars in general. This paper shows that ‘tactful ’ recursive backup parsing can be efficient, in spite of its worst case exponential time complexity. This ‘tact ’ however, should not be supplied by the grammar writer, but automatically deduced by a parser generator. In this paper we will discuss the deduction process for a simple form of two-level grammars: Affix Grammars over Finite Lattices (AGFLs), a formalism to express the syntax of natural languages. 1