Affiliation:
1. University of San Francisco, San Francisco, CA, USA
2. Tufts University, Boston, MA, USA
Abstract
Despite the power of Parser Expression Grammars (PEGs) and GLR, parsing is not a solved problem. Adding nondeterminism (parser speculation) to traditional
LL
and
LR
parsers can lead to unexpected parse-time behavior and introduces practical issues with error handling, single-step debugging, and side-effecting embedded grammar actions. This paper introduces the
LL
(*) parsing strategy and an associated grammar analysis algorithm that constructs
LL
(*) parsing decisions from ANTLR grammars. At parse-time, decisions gracefully throttle up from conventional fixed k>=1 lookahead to arbitrary lookahead and, finally, fail over to backtracking depending on the complexity of the parsing decision and the input symbols.
LL
(*) parsing strength reaches into the context-sensitive languages, in some cases beyond what GLR and PEGs can express. By statically removing as much speculation as possible,
LL
(*) provides the expressivity of PEGs while retaining
LL
's good error handling and unrestricted grammar actions. Widespread use of ANTLR (over 70,000 downloads/year) shows that it is effective for a wide variety of applications.
Publisher
Association for Computing Machinery (ACM)
Subject
Computer Graphics and Computer-Aided Design,Software
Cited by
56 articles.
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