Search results
Results from the WOW.Com Content Network
However, parser generators for context-free grammars often support the ability for user-written code to introduce limited amounts of context-sensitivity. (For example, upon encountering a variable declaration, user-written code could save the name and type of the variable into an external data structure, so that these could be checked against ...
The Syntax Definition Formalism (SDF) is a metasyntax used to define context-free grammars: that is, a formal way to describe formal languages. It can express the entire range of context-free grammars. Its current version is SDF3. [1] A parser and parser generator for SDF specifications are provided as part of the free ASF+SDF Meta Environment.
Context-free parsing for Chomsky normal form grammars was shown by Leslie G. Valiant to be reducible to Boolean matrix multiplication, thus inheriting its complexity upper bound of O(n 2.3728639). [ 16 ] [ 17 ] [ b ] Conversely, Lillian Lee has shown O ( n 3−ε ) Boolean matrix multiplication to be reducible to O ( n 3−3ε ) CFG parsing ...
A parsing expression language is a set of all strings that match some specific parsing expression. [1]: Sec.3.4 A parsing expression grammar is a collection of named parsing expressions, which may reference each other. The effect of one such reference in a parsing expression is as if the whole referenced parsing expression was given in place of ...
It is simple to extend it into a parser that also constructs a parse tree, by storing parse tree nodes as elements of the array, instead of the boolean 1. The node is linked to the array elements that were used to produce it, so as to build the tree structure. Only one such node in each array element is needed if only one parse tree is to be ...
Spirit allows for both scannerless and scanner-based parsing. SBP is a scannerless parser for Boolean grammars (a superset of context-free grammars), written in Java. Laja is a two-phase scannerless parser generator with support for mapping the grammar rules into objects, written in Java.
On the other hand, in the expressions evaluated by #expr and #ifexpr, Boolean operators like and, or, and not interpret the numerical value 0 as false and any other number as true. In terms of output, Boolean operations return 1 for a true value and 0 for false (and these are treated as ordinary numbers by the numerical operators).
Depending upon the type of parser that should be generated, these routines may construct a parse tree (or abstract syntax tree), or generate executable code directly. One of the earliest (1964), surprisingly powerful, versions of compiler-compilers is META II , which accepted an analytical grammar with output facilities that produce stack ...