Dice::nom

Another dice generator to turn text representation of dice rolls into generators. The command line interface includes many common operators; exploding dice, target numbers, success levels, etc..

Dice Operators

• ! - Explode. Reroll the dice if all the original dice are maximum value (e.g. 3d4!). An optional value can be supplied and the dice are rerolled if they are all greater than or equal to the value.
• !! - Explode Until. Same as explode, but keep rolling so long as all dice are maximum values
• * - Explode Each. Reroll any die that is the maximum value
• ** - Explode Each Until . Same as explode each, but keep rolling so long as the die is a maximum value. An optional value can be supplied and the die is rerolled if it is greater than or equal to the value.
• ++<n> - Add Each. Add the given value to each die rolled.
• --<n> - Subtract Each. Subtract the given value from each die rolled.
• `<n> - Take Low. Given a dice pool, keep the lowest N values.
• ^<n> - Take High. Given a dice pool, keep the highest N values.
• ~<n> - Take Middle. Given a dice pool, keep the middle N values.
• ADV - Advantage. Roll the dice pool twice, keeping the higher pool.
• DIS - Disadvantage. Roll the dice pool twice, keeping the lower pool.
• Y - Best Group. Keep the largest group of identical values from the pool. Keep the higher value if two groups are the same size. (e.g. 5d6Y: 3, 3, 4, 4, 1 = 8)

Arithmetic Operators

• + - Addition is assumed and can be ommited. 2d4 + 2d6 is equivalent to 2d4 2d6.
• - - Subtraction inverts the values of the dice rolled and applies to both target hits and sums. For example, the string 2d4 - 2d4[3] returns the number of successes in the first pool minus the number of successes in the second pool.

Target Operators

• [<n>] - Target High. Rolls greater then or equal to the given value are hits and are given a value of 1, others are given a value of 0.
• (<n>) - Target Low. Rolls less than or equal to the given value are hits and are given a value of 1, others are given a value of 0.
• {<n>, <m>} - Success. If the total rolled equals or exceeds <n> score 1, adding 1 for each additional <m> rolled. {<n>} is the same as {<n>, 1}. Unlike the target operators, this operator is calcualted against the complete dice score.

Comparison Operators

Two pools can be compared using the >, <, >=, <=, and = which return 1 for success and 0 for failure. In addition the comparison <=> return -1 if the left side is less than the right side, 1 if the right side is greater and 0 if they are equal.

Usage

> roll --help
roll 0.1.0
Generates random dice rolls

USAGE:
    roll [OPTIONS] <INPUT>

FLAGS:
    -h, --help       Prints help information
    -V, --version    Prints version information

OPTIONS:
    -n, --count <count>        Run the generator count number of times.
    -d, --display <display>    Display the results: full, value, or chart

ARGS:
    <INPUT>    A dice roll expression is required.

Expression

Display the generator, the individual dice rolled, and the calculated value. The expression (or at least the part that was successfully parsed) if first, followed by the dice rolls. * indicates a bonus die roll and - after the value indicates that the roll was dicarded. The total (excluding discarded rolls) is diplayed level. If a success operator is used, the level of success if displayed between {}.

> roll -n 3 3d4\*\*\{6\}
3d4**{6}: 1, 2, 3 = 6 {1}
3d4**{6}: 2, 1, 2 = 5 {0}
3d4**{6}: 4, 4*, 4*, 3*, 4, 1*, 2 = 22 {17}

Values

Display the rolled value. One value per line.

> roll -n 2 -d value 3d6
12
8

Chart

Generate a histogram of values. First column is value. Second column is the percentage chance to get that value or higher.

> roll -n 1000000 -d chart 4d6\^3
  3. 100.0: *
  4.  99.9: **
  5.  99.6: ***
  6.  98.8: *******
  7.  97.2: ************
  8.  94.3: *******************
  9.  89.5: ***************************
 10.  82.5: ************************************
 11.  73.0: ********************************************
 12.  61.6: *************************************************
 13.  48.8: ***************************************************
 14.  35.5: ***********************************************
 15.  23.1: **************************************
 16.  13.0: ****************************
 17.   5.8: ****************
 18.   1.6: *******

TODO

• library interface
• color code the results to the terminal (discards red, bonus green, etc)
• should rand::thread_rng() be moved out of Value struct? NOTE: passing in a random number generator as opposed to initializing it for each roll only resulted in a roughly 6% increase in performance
• arithmetic operators don't appear to be working

Development Notes

This is another take on a dice roller attempting to use a slightly more formal generator definition. This was also an opportunity to use the rust nom library.