Reverse Polish Notation Calculator for the commandline

This is a small commandline calculator which takes its input in reverse polish notation form.

It has an unlimited stack, supports various stack manipulation commands, can be used interactively or via a pipe and has a collector mode. It doesn't have any other dependencies than Perl.

Usage

Calculate the summary resistance of parallel resistors with 220, 330 and 440 Ohm using the following formula:

1 / (1/R1 + 1/R2 + 1/R3)

Here's the sample session:

 0 % 1
stack    1: 1

 1 % 1
stack    2: 1
stack    1: 1

 2 % 220
stack    3: 1
stack    2: 1
stack    1: 220

 3 % /
stack    2: 1
stack    1: 0.00454545454545455

=> 0.00454545454545455

 2 % 1
stack    3: 1
stack    2: 0.00454545454545455
stack    1: 1

 3 % 330
stack    4: 1
stack    3: 0.00454545454545455
stack    2: 1
stack    1: 330

 4 % /
stack    3: 1
stack    2: 0.00454545454545455
stack    1: 0.00303030303030303

=> 0.00303030303030303

 3 % 1
stack    4: 1
stack    3: 0.00454545454545455
stack    2: 0.00303030303030303
stack    1: 1

 4 % 440
stack    5: 1
stack    4: 0.00454545454545455
stack    3: 0.00303030303030303
stack    2: 1
stack    1: 440

 5 % /
stack    4: 1
stack    3: 0.00454545454545455
stack    2: 0.00303030303030303
stack    1: 0.00227272727272727

=> 0.00227272727272727

 4 % +
stack    3: 1
stack    2: 0.00454545454545455
stack    1: 0.0053030303030303

=> 0.0053030303030303

 3 % +
stack    2: 1
stack    1: 0.00984848484848485

=> 0.00984848484848485

 2 % /
stack    1: 101.538461538462

=> 101.538461538462

The % character denotes the interactive prompt. What we basically entered was:

1 1 220 / 1 330 / 1 440 / + + /

Which translates to:

1 ((1 / 220) + (1 / 330) + (1 / 440))

So, you're entering the numbers and operators as you would do on paper. To learn more, refer to the Wikipedia page linked above.

Collector mode

Beside traditional RPN you can also enter a special mode, called collector mode by entering the ( command. The collector mode has its own stack (a sub stack) which is independed of the primary stack. Inside this mode you can use all operators, however they work on ALL items on the sub stack.

So, let's compare. If you had in normal RPN mode the following stack:

3
5
6

and then entering the + operator, the calculator would pop 5 and 6 from the stack, add them and push the result 11 back to the stack.

However, if you are in collector mode with this stack, then all the items would be added, the sub stack would be cleared and the result 14 would be added to the primary stack.

You will leave the collector mode after an operator has been executed. But you can also just leave the collector mode with the command ) leaving the sub stack intact. That is, upon re-entering collector mode at a later time, you'll find the unaltered sub stack of before.

Undo

Every operation which modifies the stack can be reversed by entering the u command. There's only one level of undo and no redo.

Using STDIN via a PIPE

If the commandline includes any operator, commands will be read from STDIN, the result will be printed to STDOUT wihout any decoration and the program will exit. Commands can be separated by whitespace or newline.

Examples:

echo "2 2" | rpnc +
(echo 2; echo 2) | rpnc +

Both commands will print 4 to STDOUT.

Complete list of all supported commands:

• c clear stack
• s show the stack
• d toggle debugging (current setting: 0)
• r reverse the stack
• R rotate the stack
• ( enter collect mode
• ) leave collect mode
• u undo last operation
• q finish (C-d works as well)
• ? print help

Supported mathematical operators:

• + add
• - substract
• / divide
• * multiply
• ^ expotentiate
• % percent
• & bitwise AND
• | bitwise OR
• x bitwise XOR
• V pull root (2nd if stack==1)

Copyleft

Copyleft (L) 2019 - Thomas von Dein. Licensed under the terms of the GPL 3.0.