Reverse Polish Notation Calculator

Versions

• 1.0.0
  • Initial version.

Introduction

RPN is a command line reverse Polish notation calculator. As such, it pushes integer and fractional numbers onto a stack, and pops them off for operations:

$ rpn
dec> 6 7
dec> show
  6
  7
dec> mul
  42

RPN accepts input from files if supplied on the command line, and automatically detects if it's part of a POSIX shell command pipeline:

$ cat input.txt
6 7
mul
$ rpn input.txt
42
$ rpn <input.txt
42
$ rpn >output.txt
6 7
mul
$ cat output.txt
42

RPN optionally accepts input directly from the command line:

$ rpn --command 6 7 mul
42

Some operations are binary like add and mul, some are unary like neg and inv, some are nullary like now, some operate on the entire stack like sum and prod. Inline help provides a hint on expected inputs and outputs:

dec> help
  Arithmetic operations:
  N N  add,+   N    Add two values
  N N  sub,-   N    Subtract two values
  N N  mul,*   N    Multiply two values
  N N  div,/   N    Divide two values
  N N  mod,%   N    Modulo two values
    N  neg     N    Find the negative
    N  inv     N    Find the inverse
  N N  pow     N    Raise to the power
    N  sqrt    N    Find the square root
    *  sum     N    Sum all values
    *  prod    N    Multiply all values
  Bitwise operations:
  N N  and     N    Bitwise AND two values
  N N  or      N    Bitwise OR two values
  N N  xor     N    Bitwise XOR two values
  N N  shl     N    Shift left (multiply by power of 2)
  N N  shr     N    Shift right (divide by power of 2)
  Time operations:
       now     N    Get the current time
    N  plain   N    Convert to a plain value
    N  delta   N    Convert to a delta value
    N  time    N    Convert to a time value
  Formatting commands:
       dec          Expect and format values as decimal
       hex          Expect and format values as hexadecimal
       sep          Include a separator
       nosep        Include no separator
    N  dp           Use fixed decimal places
       nodp         Use free decimal places
  Stack commands:
    *  c(lear)      Remove all values from the stack
    N  p(op)        Remove a value from the stack
    N  d(up)   N N  Duplicate a value on the stack
  N N  s(wap)  N N  Swap two values on the stack
    N  cut          Cut a value to the internal clipboard
    N  copy    N    Copy a value to the internal clipboard
       paste   N    Paste a value from the internal clipboard
  History commands:
       u(ndo)       Undo the last operation
       r(edo)       Redo the next operation
       h(ist)       Show all undo/redo history
  General commands:
       show         Show all values on the stack
       help         Show this help text

Feature requests are welcome, but it's a hobby project in a language I don't get to use in my day job, so I prefer to do all the development myself.

Features

Arithmetic Operations

The add operation adds two values:

dec> 5.5 2.5 show
  5.5
  2.5
dec> add
  8

The sub operation subtracts two values:

dec> 5.5 2.5 show
  5.5
  2.5
dec> sub
  3

The mul operation multiplies two values:

dec> 5.5 2.5 show
  5.5
  2.5
dec> mul
  13.75

The div operation divides two values:

dec> 5.5 2.5 show
  5.5
  2.5
dec> div
  2.2

The mod operation divides two values and finds the remainder:

dec> 5.5 2.5 show
  5.5
  2.5
dec> mod
  0.5

The neg operation finds the negative:

dec> 8 show
  8
dec> neg
  -8

The inv operation finds the inverse:

dec> 8 show
  8
dec> inv
  0.125

The pow operation raises to the power:

dec> 3 4 show
  3
  4
dec> pow
  81

The sqrt operation finds the square root:

dec> 100 show
  100
dec> sqrt
  10

The sum operation sums all values on the stack:

dec> 1 2 3 4 show
  1
  2
  3
  4
dec> sum
  10

The prod operation multiplies all values on the stack:

dec> 1 2 3 4 show
  1
  2
  3
  4
dec> prod
  24

Bitwise Operations

The and operation performs a bitwise AND on all bits:

dec> hex
hex> ffff ff00ff show
  0000ffff
  00ff00ff
hex> and
  000000ff

The or operation performs a bitwise OR on all bits:

dec> hex
hex> ffff ff00ff show
  0000ffff
  00ff00ff
hex> or
  00ffffff

The xor operation performs a bitwise XOR on all bits:

dec> hex
hex> ffff ff00ff show
  0000ffff
  00ff00ff
hex> xor
  00ffff00

The shl operation shifts left, i.e. multiplies by a power of 2:

dec> 16 4 show
  16
  4
dec> shl
  256

The shr operation shifts right, i.e. divides by a power of 2:

dec> 16 4 show
  16
  4
dec> shr
  1

Time Operations

The now command gets the current time, showing times in UTC:

dec> now
  2024-03-02T11:37:15.724

The plain command converts to an integer or fractional value:

dec> now
  2024-03-02T11:37:15.724
dec> plain
  1709379435.724

The delta command converts to a delta value, optionally showing days, hours, minutes, seconds and milliseconds:

dec> 86399 show
  86399
dec> delta
  23:59:59.000

The time command converts to a time value, showing times in UTC:

dec> 1709294400 show
  1709294400
dec> time
  2024-03-01T12:00:00.000

Delta values can be added to or subtracted from times:

dec> 1709294400 time 86400 delta
  2024-03-01T12:00:00.000
           1:00:00:00.000
dec> sub
  2024-02-29T12:00:00.000

One time value can be subtracted from another:

dec> 1709294400 time 1709208000 time
  2024-03-01T12:00:00.000
  2024-02-29T12:00:00.000
dec> sub
  1:00:00:00.000

Formatting Commands

The dec and hex commands expect and format values as decimal and hexadecimal:

dec> 2 32 pow hex
  0000000100000000
hex> dec
  4294967296

The sep and nosep commands show and hide a separator for decimal and hexadecimal:

dec> 2 32 pow hex sep
  00000001 00000000
hex> dec
  4,294,967,296

The dp and nodp commands set and cancel fixed precision for decimal:

dec> 2 sqrt
  1.4142135623730951454746218587388284504413604736328125
dec> 0 dp
  1
dec> 3 dp
  1.414
dec> 6 dp
  1.414214
dec> nodp
  1.4142135623730951454746218587388284504413604736328125

Stack Commands

The clear command removes all values from the stack:

dec> 1 23 456 show
  1
  23
  456
dec> clear

The pop command removes a value from the stack:

dec> 1 23 456 show
  1
  23
  456
dec> pop
  1
  23

The dup command duplicates a value on the stack:

dec> 1 23 456 show
  1
  23
  456
dec> dup
  1
  23
  456
  456

The swap command swaps two values on the stack:

dec> 1 23 456 show
  1
  23
  456
dec> swap
  1
  456
  23

The cut and copy commands store a value from the stack in the internal clipboard. The paste command copies that value back to the stack:

dec> 1 23 show
   1
  23
dec> copy
dec> 456 show
    1
   23
  456
dec> paste
    1
   23
  456
   23

History Commands

The undo and redo commands undo the last operation, and redo the next operation in the history:

dec> 1 23 456 show
    1
   23
  456
dec> prod
  10488
dec> undo
    1
   23
  456
dec> undo
dec> redo
    1
   23
  456
dec> redo
  10488

The hist command shows all undo/redo history:

dec> 1 23 456 show
    1
   23
  456
dec> prod
  10488
dec> undo
    1
   23
  456
dec> hist
  1 23 456
  <==
  prod