222 research outputs found
Left Recursion in Parsing Expression Grammars
Parsing Expression Grammars (PEGs) are a formalism that can describe all
deterministic context-free languages through a set of rules that specify a
top-down parser for some language. PEGs are easy to use, and there are
efficient implementations of PEG libraries in several programming languages.
A frequently missed feature of PEGs is left recursion, which is commonly used
in Context-Free Grammars (CFGs) to encode left-associative operations. We
present a simple conservative extension to the semantics of PEGs that gives
useful meaning to direct and indirect left-recursive rules, and show that our
extensions make it easy to express left-recursive idioms from CFGs in PEGs,
with similar results. We prove the conservativeness of these extensions, and
also prove that they work with any left-recursive PEG.
PEGs can also be compiled to programs in a low-level parsing machine. We
present an extension to the semantics of the operations of this parsing machine
that let it interpret left-recursive PEGs, and prove that this extension is
correct with regards to our semantics for left-recursive PEGs.Comment: Extended version of the paper "Left Recursion in Parsing Expression
Grammars", that was published on 2012 Brazilian Symposium on Programming
Language
Purely functional GLL parsing
Generalised parsing has become increasingly important in the context of software language design and several compiler generators and language workbenches have adopted generalised parsing algorithms such as GLR and GLL. The original GLL parsing algorithms are described in low-level pseudo-code as the output of a parser generator. This paper explains GLL parsing differently, defining the FUN-GLL algorithm as a collection of pure, mathematical functions and focussing on the logic of the algorithm by omitting implementation details. In particular, the data structures are modelled by abstract sets and relations rather than specialised implementations. The description is further simplified by omitting lookahead and adopting the binary subtree representation of derivations to avoid the clerical overhead of graph construction.
Conventional parser combinators inherit the drawbacks from the recursive descent algorithms they implement. Based on FUN-GLL, this paper defines generalised parser combinators that overcome these problems. Th
Jparsec - a parser combinator for Javascript
Parser combinators have been a popular parsing approach in recent years. Compared with traditional parsers, a parser combinator has both readability and maintenance advantages.
This project aims to construct a lightweight parser construct library for Javascript called Jparsec. Based on the modular nature of a parser combinator, the implementation uses higher-order functions. JavaScript provides a friendly and simple way to use higher-order functions, so the main construction method of this project will use JavaScript\u27s lambda functions. In practical applications, a parser combinator is mainly used as a tool, such as parsing JSON files.
In order to verify the utility of parser combinators, this project uses a parser combinator to parse a partial Lua grammar. Lua is a widely used programming language, serving as a good test case for my parser combinator
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