This directory contains simple examples of Bison grammar files in C.
Some of them come from the documentation, which should be installed together with Bison. The URLs are provided for convenience.
The first example is that of a simple double-precision Reverse Polish Notation calculator (a calculator using postfix operators). This example provides a good starting point, since operator precedence is not an issue.
Extracted from the documentation: “Reverse Polish Notation Calculator” https://www.gnu.org/software/bison/manual/html_node/RPN-Calc.html
This example is slightly more complex than rpcalc: it features infix operators (1 + 2, instead of 1 2 + in rpcalc), but it does so using a unambiguous grammar of the arithmetic instead of using precedence directives (%left, etc.).
A more complete C example: a multi-function calculator. More complex than the previous example. Using precedence directives to support infix operators.
Extracted from the documentation: “Multi-Function Calculator: mfcalc”. https://www.gnu.org/software/bison/manual/html_node/Multi_002dfunction-Calc.html
The calculator, redux. This time using a scanner generated by Flex.
The example builds on top of the previous one to provide a reentrant parser. Such parsers can be called concurrently in different threads, or even recursively. To demonstrate this feature, expressions in parentheses are tokenized as strings, and then recursively parsed from the parser. So (((1)+(2))*((3)+(4))) uses eight parsers, with a depth of four.