rbison is a clear and simple alternative to GNU Bison. it takes a context-free grammar and generates an LALR(1) parser. with a clean and small codebase, rbison is easy to read, understand, and extend - great for learning and exploring how parser work.

$ cd src && make
$ ./rbison 
rbison 0.02 [gcc 12.2.0] [Jul 22 2025]. (c) 2025, ****. all rights reserved.
usage is: rbison [-options] file

  create an LALR(1) parser from the specification in the
  input file. legal command-line options are:

-a   output actions only (see -p)
-l   suppress #(L)ine directives
-p   output parser only (can be used with -T also)
-s   make (s)ymbol table
-S   make more-complete (S)ymbol table
-t   print all (T)ables (and the parser) to standard output
-T   move large tables from y.tab.c to y.outab.c
-v   print (V)erbose diagnostics (including symbol table)
-V   more verbose than -v. implies -t, & y.output goes to stderr
-w   suppress all warning messages
-W   warnings (as well as errors) generate nonzero exit status

this section shows how to run a calculator built with rbison.

rbison uses rlex to generate the lexer. please install rlex first:

$ git clone https://github.com/remysys/rlex.git
$ cd rlex/src
$ make && make install

the test/ directory contains five examples: expr_1 to expr_5. each example consists of a .l file and a .y file:

• the .l file defines lexical rules and is processed by rlex to generate the lexer.
• the .y file defines grammar rules and is compiled by rbison to generate the parser.

these examples show how rbison and rlex work together to build expression calculators with support for basic math, operator precedence, and floating-point numbers.

run make test to build five calculator examples in the test/ directory.

$ make test

to try out one of the calculator demos:

$ ./expr_1

then enter an expression like:

$ 6 + 6 + 2 * 3

the program will evaluate the expression and print the result:

$ res = 18