This is a simple experimental parser for dice expressions like 1d20, 4d6 and 5d8.

The parser currently supports normal dice rolls, scalar numbers, operations (only addition and subtraction for now) and modifiers (keep the highest, drop the lowest, etc).

While not in active development, I share this code hoping you find this concept interesting.

[TOC]

You can parse expressions like 1d20 using the cli and get a result.

# usage
# criticalSuccess <roll> [-p|--prefix]...

criticalSuccess 1d20
# 15

If the expression has spaces, you have to wrap them in " like

criticalSuccess "3d6 + 1"
# 14

You can roll multiple sets of dice by giving multiple expressions separated by spaces or using the a semi-colon symbol ;. The results will appear line by line.

# you can use spaces
# criticalSuccess 1d20 "d6 + 1" 5d8
# or semi-colons
# criticalSuccess "1d20 ; d6 + 1 ; 5d8"
# or both
# criticalSuccess "1d20 ; d6 + 1" 5d8
# all of the above are equivalent:

criticalSuccess 1d20 "d6 + 1" 5d8
# 3
# 4
# 22

You could also use the ; symbol to separate expressions in a single string.

criticalSuccess "1d20 ; d6 + 1"
# equivalent to criticalSuccess "1d20 ; d6 + 1"
# 3
# 4

By giving the -p|--prefix option (it has to be at the end), each result will appear prefixed by its expressions.

criticalSuccess "2d20H + 1d4" 3d6 -p
# 2d20H + 1d4: 21
# 3d6: 10

If there is an error in any of the expressions, you will get best description of the problem.

criticalSuccess dd
# Syntax error at position 1: number in range [-2147483648, 2147483647] expected, but found DSymbol.
# dd
#  ^

The command can spawn an interactive shell using the option cli.

criticalSuccess cli
Enter an expression or a command and press enter
Commands: [c] to close the shell, [?] to print this message
> 2d10
# 9
> 5d8
# 21
> c
# exits
# you can also press Ctrl + C to exit

Below is a table establishing desired rolls and their expressions.

The syntax is meant to read dice rolls like you would find in TTRPGs (Table Top Roll Playing Games). Therefore, a string of characters like 4d6 means roll four six-sided dice and sum the results.

The parser accepts any expression of the form [number of dice]d<number of sides>[modifier] where [number of dice] is a number between 0 and 255 (inclusive), <number of sides> is a number between -2147483648 and 2147483647 (also inclusive) and [modifier] changes the way in the results are added up. In case [number of dice] is 1, you can simplify the expression to d<number of sides>. You can read more about dice with a negative number of sides here) and check the available modifiers below.

Other considerations:

• you can add or subtract any scalar number for a die (1d6 + 1 will roll one d6 and add 1 to the result).
• the grammar ignores spaces, so 1 d 20 and 2 + 1 are equivalent to 1d20 and 2+1 respectively.
• the d in any dice expression is case insensitive, meaning d20 and 4d6 are equivalent to D20 and 4D6 respectively.
• You can separate expressions using the special symbol ;.

At the end of any dice expression, you can use one of the following modifiers:

• H only keeps the highest result. If you roll any number of dice, only the highest value will be kept.
• L only keeps the lowest result. If you roll any number of dice, only the lowest value will be kept.
• h drops the highest result. If you roll any number of dice, the highest will be ignored.
• l drops the lowest result. If you roll any number of dice, the lowest will be ignored.
• e explotes any single die in the result. For any number of dice you roll if you get the lowest or highest value possible on that die, roll an additional die of the same type. Note that the rule applies for any additional die you roll, so in theory you could get an infinite loop.:

The formal grammar can be found in this document.

You can write expressions like 1d-4 and you will get a number between -4 and -1. It is equivalent to writing 0 - 1d4.

The whole project is develop in C#. The src folder holds the Solution and the Projects with the components of the applications.

MIT License