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This paper describes an approach for determining the minimum, maximum, and average times to parse sentences acceptable by a deterministic parser. These quantities are presented in the form of symbolic formulas, called time-formulas. The variables in these formulas represent not only the length of the input string but also the time to perform elementary operations such as pushing, popping, subscripting, iterating, etc. By binding to the variables actual numerical values corresponding to a given compiler-machine configuration, one can determine the execution time for that configuration. Time-formulas are derived by examining the grammar rules and the program representing the algorithm one wishes to analyze. The approach is described by using a specific grammar that defines simple arithmetic expressions. Two deterministic parsers are analyzed: a top-down recursive descent LL(1) parser, and a bottom-up SLR(1) parser. The paper provides estimates for the relative efficiencies of the two parsers. The estimates applicable to a specific machine, the PDP-10, are presented and substantiated by benchmarks. Finally, the paper illustrates the proposed approach by applying it to the analyses of parsers for a simple programming language.

Described is a method for syntactic error recovery that is compatible with deterministic parsing methods and that is able to recover from many errors more quickly than do other schemes because it performs global context recovery. The method relies on fiducial symbols, which are typically reserved key words of a language, to provide mileposts for error recovery. The method has been applied to LL(1) parsers, for which a detailed algorithm is given, and informally proved correct. The algorithm will always recover and return control to the parser if the text being analyzed satisfies only minimal requirements: that it contains one or more occurrences of fiducial symbols following the point at which an error is detected. Tables needed for error recovery have been automatically generated, along with parsing tables, by a parser constructor for the LL(1) grammars. A theoretical characterization of fiducial symbols is given, and the utility of this characterization in practice is discussed. It has been applied to a grammar for the programming language Pascal to aid in selection of a set of fiducial symbols. The error recovery scheme has been tested on a set of student-written Pascal program texts and is compared with other error recovery strategies.