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A predictive parser is a recursive descent parser that does not require backtracking. [3] Predictive parsing is possible only for the class of LL( k ) grammars, which are the context-free grammars for which there exists some positive integer k that allows a recursive descent parser to decide which production to use by examining only the next k ...
A formal grammar that contains left recursion cannot be parsed by a LL(k)-parser or other naive recursive descent parser unless it is converted to a weakly equivalent right-recursive form. In contrast, left recursion is preferred for LALR parsers because it results in lower stack usage than right recursion.
With many levels of precedence, implementing this grammar with a predictive recursive-descent parser can become inefficient. Parsing a number, for example, can require five function calls: one for each non-terminal in the grammar until reaching primary. An operator-precedence parser can do the same more efficiently. [1]
A TDPL grammar can be viewed as an extremely minimalistic formal representation of a recursive descent parser, in which each of the nonterminals schematically represents a parsing function. Each of these nonterminal-functions takes as its input argument a string to be recognized, and yields one of two possible outcomes:
Tail recursive parsers are commonly used to parse left recursive grammars. They use a smaller amount of stack space than regular recursive descent parsers. They are also easy to write. Typical recursive descent parsers make parsing left recursive grammars impossible (because of an infinite loop problem). Tail recursive parsers use a node ...
parboiled is commonly used as an alternative for regular expressions or parser ... complete recursive descent parser with ... Example of a complete Java 6 parser ...
Since Packrat is a recursive descent parser, it cannot handle left recursion directly. [5] During the early stages of development, it was found that a production that is left-recursive can be transformed into a right-recursive production. [6] This modification significantly simplifies the task of a Packrat parser.
The example uses no token look ahead at all and thus is not really helpful to understand the strength of recursive descent parsers. There should at least be a bit of ambiguity in the grammar, otherwise the example is too trivial and - even worse - points the reader into wrong directions.