# roll.py: A dice-rolling simulator for RPGs

This was a weekend hobby project inspired by [Critical Role][1] and
other D&D shows and podcasts. While a dice simulator is no substitute
for physically rolling real dice, it might be useful for anyone who's
on the go or otherwise unable to access their dice and a flat surface
to roll them on (or for new players who want to try out RPGs without
having to spend money on dice first). It supports almost everything in
the ["Standard Notation"][2] section of the Wikipedia page on dice
notation, as well as the syntax in this online [RPG Dice Roller][3]
and this [Android App][4].

[1]: http://geekandsundry.com/shows/critical-role/
[2]: https://en.wikipedia.org/wiki/Dice_notation#Standard_notation
[3]: http://rpg.greenimp.co.uk/dice-roller/
[4]: https://www.critdice.com/roll-advanced-dice

## Usage

There are two ways to use this script. Either run it with any number
of arguments, which will be concatenated and rolled, or run it with no
arguments to enter interactive mode, where you can type a roll on each
line and hit enter to roll it. In either case, the last line indicates
the total roll, and all the lines before it indicate the individual
dice rolls that led to it. Examples:

```bash
# Single-roll command-line mode
$ ./roll.py 2d4+2
2d4 rolled: [3,1], Total: 4
2017-11-26 15:54:47,849 INFO: Total roll for '2d4 + 2': 6
# Interactive mode
$ ./roll.py
# Advantage roll in D&D, with a modifier
Enter roll> 2d20-L+2
2d20-L rolled: 10 (dropped 5)
2017-11-26 15:55:37,826 INFO: Total roll for '2d20-L + 2': 12

Enter roll> 6d6+6
6d6 rolled: [4,4,6,5,6,2], Total: 27
2017-11-26 16:26:43,989 INFO: Total roll for '6d6 + 6': 33

Enter roll> d100
d100 rolled: 16
2017-11-26 16:26:51,805 INFO: Total roll for 'd100': 16

# Complex arithmetic expressions and non-standard dice are allowed
Enter roll> d4 + 2d6 + 4 - 3d8 + 6d7/2
d4 rolled: 1
2d6 rolled: [3,6], Total: 9
3d8 rolled: [4,5,5], Total: 14
6d7 rolled: [1,3,4,1,4,6], Total: 19
2017-11-26 16:27:01,238 INFO: Total roll for 'd4 + 2d6 + 4 - 3d8 + (6d7 / 2)': 9.5

# Any arithmetic expression is allowd, even if it doesn't roll any dice
Enter roll> 4 + 6^2 / 3
2017-11-26 16:48:46,121 INFO: Total roll for '4 + ((6 ^ 2) / 3)': 16

# You can save specific rolls as named variables
Enter roll> health_potion = 2d4 + 2
2017-11-26 16:53:56,188 INFO: Saving health_potion as '2d4 + 2'

Enter roll> health_potion
2d4 rolled: [1,3], Total: 4
2017-11-26 16:54:44,287 INFO: Total roll for '2d4 + 2': 6

# Variables can reference other variables
Enter roll> greater_health_potion = health_potion + health_potion
2017-11-26 16:54:12,684 INFO: Saving double_health_potion as 'health_potion + health_potion'

Enter roll> greater_health_potion
2d4 rolled: [4,4], Total: 8
2d4 rolled: [4,3], Total: 7
2017-11-26 16:55:30,455 INFO: Total roll for '(2d4 + 2) + (2d4 + 2)': 19

# Show currently defined variables
Enter roll> vars
2017-11-26 16:59:15,241 INFO: Currently defined variables:
greater_health_potion = 'health_potion + health_potion'
health_potion = '2d4 + 2'

# Delete a variable
Enter roll> del greater_health_potion
2017-11-26 16:59:40,713 INFO: Deleting saved value for 'greater_health_potion'.

# Reroll ones once
Enter roll> 4d4r
4d4r rolled: [1r,2,2,3], Total: 8
2017-11-26 17:01:41,592 INFO: Total roll for '4d4r': 8

# Reroll ones indefinitely
Enter roll> 4d4R
4d4R rolled: [3,3,2R,4], Total: 12
2017-11-26 17:01:53,784 INFO: Total roll for '4d4R': 12

# Exploding dice
Enter roll> 6d6!
6d6! rolled: [1,6!,3,3,4,5,6!,5], Total: 33
2017-11-26 16:30:43,003 INFO: Total roll for '6d6!': 33

# Explode any roll greater than 3
Enter roll> 6d6!>3
6d6!>3 rolled: [4!,4!,6!,2,2,5!,2,1,6!,4!,1,1], Total: 38
2017-11-26 16:32:18,204 INFO: Total roll for '6d6!>3': 38

# Penetrating dice
Enter roll> 6d6!p
6d6!p rolled: [1,6!p,1,5,6!p,2,1,5], Total: 27
2017-11-26 16:32:48,727 INFO: Total roll for '6d6!p': 27

# Fate dice
Enter roll> 4dF+2
4dF rolled: [0,0,0,1], Total: 1
2017-11-26 16:34:11,533 INFO: Total roll for '4dF + 2': 3

# Enter 'help' for other non-roll commands
Enter roll> quit
2017-11-26 16:29:47,624 INFO: Quitting.
```

As you can see, it not only reports the total for each roll, but all
the individual dice rolls as well, so you can understand how it came
up with the total. This also lets you figure out whether you rolled a
natural 20 or natural 1 on the die for critical hits and misses, and
if your damage roll involves multiple different kinds of damage, it
lets you figure out how much of each damage type was dealt.

## Known Issues

* There is no sanity checking for dice roll effects that will never
  take effect, such as exploding a d6 on 7 (i.e. `d6!=7)
* Error messages are pretty much just reported as is, with no attempt
  to explain or contextualize them.