## Reverse Polish Notation Calculator for the commandline
This is a small commandline calculator which takes its input in
[reverse polish notation](https://en.wikipedia.org/wiki/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.