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https://github.com/ezaquarii/bison-flex-cpp-example

GNU Bison and GNU Flex C++ example
https://github.com/ezaquarii/bison-flex-cpp-example

bison bison-grammar compiler flex yacc

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GNU Bison and GNU Flex C++ example

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README 

        
#Flex & Bison LALR C++ example#



## What? ##



This is a not-so-crude example showing how to deploy *Flex* and *GNU Bison* in modern C++ programs. Example program provides simple commandline that parses function calls with list of arguments (unsigned ints only) and builds AST. AST is printed when parsing completes. See code comments for more details.



Features:



* Compatible with the good, old `C++03` for maximum portability.

* Fully reentrant parser and lexer, C++ implementation.

* Parser and lexer are in a customized namespace with custom class names.

* Flex base class has a customized name; multiple different flex scanners in the binary are possible without a name conflict. Believe it or not, but even in the 21st century it is still a bit tricky with *Flex*.

* Parser and scanner enclosed in a "driver" class (`Interpreter`)

* Uses *Bison 3.0* token variant API (yay!).

* Location tracking. Not perfect, but the core is there.



Once we overcome the abovementioned obstacles, the *Flex/GNU Bison* pair becomes quite pleasant to use in day to day work.



## Disclaimer ##

  

Haven't tested it on *MS Windows*. Please tell me if it works there... Do not forget to turn off `unistd.h` in options.



## Why bother? ##



Official *GNU Bison* example features C++ parser connected to primitive C-style lexer, which is probably not what you want most of the time. There is currently (2014) no easy way to find a true C++ example of elegant *Flex/Bison3* deployment. I really do not understand why a serious project like *Bison* provides such a poor user-experience for beginners.



##Yea, but still, why bother with old Flex/Bison?##



*ANTLR4* has been released without C++ support nor any estimation (last checked September 2014). The *Java* generator is premium quality though.



*ANTRL3* explicitly states that C++ support is total garbage and the mailing lists didn't make my impression any better.



*Flexc++* and *Bisonc++* are not that popular. I wasn't sure about portability either.



*Flex* and *GNU Bison* don't pull any dependencies and the code is (or at least is claimed to be) portable. By "portable" I mean it works in *Unix* universe and *Windows*, because the latter one is the only platform on the planet being notorious for catastrophically imbecilic design decisions (`cmd.exe`, `http:\\www.microsoft.com\backslash\fetish`, etc), causing endless, epic portability issues and developer's nightmares.



## Source organization ##



The main function creates the `Interpreter` object and calls `parse()`. `Scanner` and `Parser` are encapsulated in the `Interpreter`. By default the `Scanner` reads the standard input, but you can switch it using the provided `Interpreter` API and feed it with an arbitrary stream, such as `std::stringstream`.



## Building ##



Crude Makefile is provided - not much...



`make`



`./a.out`



`make clean`



## Legal mumbo-jumbo ##



The example code is MIT-licensed. The code generated by *Flex* and *Bison* has a separate license: Modified, non-viral GPL, which is safe to use. See the source code files.



## TODO ##



* some kind of template to deploy a complete scanner/parser stub in a project with an IDE wizard

* namespace defined with preprocessor?



## Special thanks ##



* My girl - for late coffees and feeding me during deep coding sessions

* *Flex* and *GNU Bison* folks - for focus on portability and years of maintenance

* MIT folks - for *MIT License*

* Me - for assembling this example



Enjoy!