tarmstrong/hrolldice

a Haskell program that rolls virtual dice, loosely based on `rolldice` by Stevie Strickland.

hrolldice

Name

hrolldice - a Haskell program that rolls virtual dice, loosely based on rolldice by Stevie Strickland.

Synopsis

hrolldice dice_string dice_string ...

Description

As an exercise in writing Haskell programs, I wrote my own version of rolldice by Stevie Strickland. It is not an exact clone, but for the majority of dice rolls it is a drop-in replacement.

dice_strings specify the number of dice, what kind of dice, how many to drop, etc. For example:

• d6: roll a six-sided die.
• 4d6: roll four six-sided die and sum the result.
• 2x4d6: same as 4d6, but perform it twice and show each result separately.
• 4d6s1: same as 4d6 but drop the lowest number rolled.
• d6*2+1: same as d6 but multiply it by 2 and then add 1
• d6+1*2: same as d6 but add 1 and then multiply the result by 2.

In other words, the "modifier functions" at the end are processed in order from left to right. +1*2-3 can be thought of as (((result + 1) * 2) - 3). This behaviour is different than rolldice, which will only handle one multiplier and one offset (it takes the last occurrence of each without saying so) and has a specified order of operations (multiplication, then addition/subtraction).

Example usage:

Roll four six-sided dice four times, dropping the lowest number. Repeat six times.

$ hrolldice 6x4d6s1

13 11 10 16 7 8

This is the typical way to generate "ability scores" in RPGs like D&D.

Prior Art

• rolldice, as mentioned above.
• python-rolldice, a python clone of rolldice.
• game-probability seems like a useful Haskell library that I would have used had I not been doing this as an exercise.

TODO

• Better error messages on incorrect dice strings.
• Tests for modifier functions.
• Better API.

Author

Tavish Armstrong [email protected]