A cmdline / stdin driven Reverse Polish Notation Calculator

This project is a complete, polished, but small product: A reverse polish notation calculator in the style of a unix command line tool.

It looks something like this:

It focuses on:

• Awareness of UNIX command line culture, convention, and user expectations
• Supports interactive use cases as well as programmatic use cases involving pipelines and redirection
• A tool that is pleasant, intuitive, and flexible
• A reasonably high degree of polish

You'll be happy to make this program a part of your permanent toolbox.

What it is:

• A tool called rpn written in python and no other dependancies.
• The command line tool that operates like other UNIX command line tools.
• Packaged so it can be easily built/run on common UNIX systems (Linux, MacOS)

References

While developing this project, we found the following references useful:

• Wikipedia: Reverse Polish Notation
• RPN Tutorial

Getting started

For example, a programmer working on a low level project might expect binary and hex input/output:

$ rpn
> bin
> 0xaa55
0b1010101001010101 > 2 |
0b1010101001010111 > 1 ~ &
0b1010101001010110 >

And someone interested in factorials may expect more than the usual level of precision:

$ rpn
> 50 fact
30414093201713375576366966406747986832057064836514787179557289984 >

These are just a couple of examples. An end user should expect to fumble around with this tool and be pleasantly surprised when things "just work".

Example: Command Line Help

This is the command line help from our reference implementation:

USAGE:

  rpn --help                   Show this help message
  rpn                          Launch in interactive mode
  rpn [expression]             Evaluate a one-line expression
  rpn help                     Show command reference (just runs the 'help' command)

RC FILES

  ~/.rpnrc is executed at startup if it exists.
  ~/.rpn_history contains the command history for interactive mode.

EXAMPLES

  rpn 1 2 + 3 + 4 + 5 +              => 15
  rpn pi cos                         => -1
  rpn                                => interactive mode