#Praser 2

This is the second incarnation of the Praser parser library. The first iteration function, but due to its parser combinator paradigm it was ill suited to being coded in C. This version is purely based on parser description files (*.pra) that use a BNF like syntax. There are three examples provided right now: src/parser.pra is the description of the description language, src/calculator.pra is a description for a subset of mathematical notation, and src/set.pra is a description for a simplified charset notation (it is basically useless but good for testing the parsers based on src/parser.pra). The goal of this library is to provide a basis for the creation of a parser for a programming language.

This distribution contains a script, parser_runner.sh, that runs various parsers and callbacks. The implementation of this script is described later. Once the library has been built, it can be run like:

./parser_runner.sh <parser> <action> <file to parse> [<action arguments>]

Where <parser> is the name of the parser to use (by default, parser and generated are built and they should have the same behavior) and <action> is what to do with the abstract syntax tree (ast) the parser returns (currently there are print to print, interpret <file to interpret> to parse a file by interpreting the ast returned by the parser description parser, and compile <output file> to generate a C source file for a parser described in <file to parse>). src/modules/generated_parser.c is generated by running ./parser_runner.sh parser compile src/parser.pra src/modules/generated_parser.c.

parser_runner.sh works by dynamically linking a glue program (src/parser_runner.c) with different shared libraries. The glue program has two functions, start_parser and ast_callback, that are provided by stub libraries that report them as missing when they are called. The shell script sets LS_PRELOAD to load different shared libraries and change start_parser and ast_callback. Unfortunately this only works on Linux, but the library itself should be cross platform so on other platforms it should be easy to just build executables for every combination of parser and callback. I may add that to the tupfile, but it is not currently a priority.

#Building

Praser 2 uses tup as its build system, but should not have any other dependencies (besides the avl tree and slab allocator libraries included in this repository and not currently used). To build Praser on Linux, simply run tup. The demonstration cannot currently be built on OSX or Windows, and because I'm using dynamic linking it probably won't be soon. Basically any solution to having multiple parsers and multiple callbacks that does not build a separate program for every combination is not cross platform and hence would require multiple implementations.