Search results
Results from the WOW.Com Content Network
These examples all only require lexical context, and while they complicate a lexer somewhat, they are invisible to the parser and later phases. A more complex example is the lexer hack in C, where the token class of a sequence of characters cannot be determined until the semantic analysis phase since typedef names and variable names are ...
Here is a very simple program in re2c (example.re). It checks that all input arguments are hexadecimal numbers. The code for re2c is enclosed in comments /*!re2c ... */, all the rest is plain C code. See the official re2c website for more complex examples. [23]
Flex (fast lexical analyzer generator) is a free and open-source software alternative to lex. [2] It is a computer program that generates lexical analyzers (also known as "scanners" or "lexers").
The code generated by Bison includes significant amounts of code from the Bison project itself. The Bison package is distributed under the terms of the GNU General Public License (GPL) but an exception has been added so that the GPL does not apply to output.
Ragel is a finite-state machine compiler and a parser generator.Initially Ragel supported output for C, C++ and Assembly source code, [4] later expanded to support several other languages including Objective-C, D, Go, Ruby, and Java. [5]
The meta language of JetPAG grammars was designed to be maximally flexible handle both simple grammars and large, complicated ones easily. Parsers and lexical analyzers are similarly defined and generated for simplicity and ease of use. This is a simple example of a grammar for a basic calculator:
This stage of a multi-pass compiler is to remove irrelevant information from the source program that syntax analysis will not be able to use or interpret. Irrelevant information could include things like comments and white space. In addition to removing the irrelevant information, the lexical analysis determines the lexical tokens of the language.
The following example demonstrates the common case of parsing a computer language with two levels of grammar: lexical and syntactic. The first stage is the token generation, or lexical analysis, by which the input character stream is split into meaningful symbols defined by a grammar of regular expressions.