dart_dice_parser

A dart library for parsing dice notation (2d6+4). Supports advantage/disadvantage, counting success/failures, exploding, compounding, and other variations.

Example


import 'package:dart_dice_parser/dart_dice_parser.dart';

void main() {
  // Create a roller for D20 advantage (roll 2d20, keep highest).
  final d20adv = DiceExpression.create('2d20 kh');

  stdout.writeln(d20adv.roll());
  // outputs:
  //  ((2d20) kh ) ===> RollSummary(total: 16, results: [16], metadata: {rolled: [4, 16], discarded: [4]})

  stdout.writeln(d20adv.roll());
  // outputs:
  //  ((2d20) kh ) ===> RollSummary(total: 19, results: [19], metadata: {rolled: [13, 19], discarded: [13]})
}

Dice Notation

Examples:

2d20 #cf #cs
- roll 2d20, result will include counts of critical successes (20) and failures (1)
advantage
- 2d20-L -- drop lowest
- 2d20k, 2d20kh -- keep highest
disadvantage
- 2d20-H -- drop highest
- 2d20-kl -- keep lowest
(2d10+3d20)-L3 -- roll 2d10 and 3d20, combine the two results lists, and drop lowest 3 results
20d10-<3->8# -- roll 20 d10, drop any less than 3 or greater than 8 and count the number of remaining dice

Supported notation

2d6 -- roll 2 dice of 6 sides
special dice variations:
- 4dF -- roll 4 fudge dice (sides: [-1, -1, 0, 0, 1, 1])
- 1d% -- roll 1 percentile dice (equivalent to 1d100)
- 1D66 -- roll 1 D66, aka 1d6*10 + 1d6
  - NOTE: you must use uppercase D66, lowercase d66 will be interpreted as a 66-sided die
exploding dice
- 4d6! -- roll 4 6-sided dice, explode if max (6) is rolled (re-roll and include in results)
  - 4d6 !=5 or 4d6!5 -- explode a roll if equal to 5
  - 4d6 !>=4 - explode if >= 4
  - 4d6 !<=2 - explode if <=2
  - 4d6 !>5 - explode if > 5
  - 4d6 !<2 - explode if <2
  - To explode only once, use syntax !o
    - 4d6 !o<5
compounding dice (Shadowrun, L5R, etc). Similar to exploding, but the additional rolls for each dice are added together as a single "roll". The original roll is replaced by the sum of it and any additional rolls.
- 5d6 !! -- roll 5 6-sided dice, compound
  - 5d6 !!=5 or 5d6!5 -- compound a roll if equal to 5
  - 5d6 !!>=4 - compound if >= 4
  - 5d6 !!<=4 - compound if <= 4
  - 5d6 !!>5 - compound if > 5
  - 5d6 !!<3 - compound if < 3
  - To compound only once, use syntax !!o
    - 5d6 !!o<2
re-rolling dice:
- 4d4 r2 -- roll 4d4, re-roll any result = 2
- 4d4 r=2 -- roll 4d4, re-roll any result = 2
- 4d4 r<=2 -- roll 4d4, re-roll any <= 2
- 4d4 r>=3 -- roll 4d4, re-roll any >= 3
- 4d4 r<2 -- roll 4d4, re-roll any < 2
- 4d4 r>3 -- roll 4d4, re-roll any > 3
- To reroll only once, use syntax ro
  - 4d4 ro<2
keeping dice:
- 3d20 k 2 -- roll 3d20, keep 2 highest
- 3d20 kh 2 -- roll 3d20, keep 2 highest
- 3d20 kl 2 -- roll 3d20, keep 2 lowest
dropping dice:
- 4d6 -H -- roll 4d6, drop 1 highest
- 4d6 -L -- roll 4d6, drop 1 lowest
- 4d6 -H2 -- roll 4d6, drop 2 highest
- 4d6 -L2 -- roll 4d6, drop 2 lowest
- 4d6 ->5 -- roll 4d6, drop any results > 5
- 4d6 -<2 -- roll 4d6, drop any results < 2
- 4d6 ->=5 -- roll 4d6, drop any results >= 5
- 4d6 -<=2 -- roll 4d6, drop any results <= 2
- 4d6 -=1 -- roll 4d6, drop any results equal to 1
- NOTE: the drop operators have higher precedence than the arithmetic operators; 4d10-L2+2 is equivalent to (4d10-L2)+2
- NOTE: drop is not subtraction.
  - 4d6 - 3 -- roll 4d6, subtract 3
  - 4d6 - 2d6 -- roll 4d6, subtract the result of rolling 2d6
cap/clamp:
- 4d20 C<5 -- roll 4d20, change any value < 5 to 5
- 4d20 C>15 -- roll 4d20, change any value > 15 to 15
scoring dice rolls:
- counting:
  - 4d6 # -- how many results?
    - For example, you might use this to count # of dice above a target. (5d10 -<6)# -- roll 5 d10, drop any less than 6, count results
  - 4d6 #>3 -- roll 4d6, count any > 3
  - 4d6 #<3 -- roll 4d6, count any < 3
  - 4d6 #>=5 -- roll 4d6, count any >= 5
  - 4d6 #<=2 -- roll 4d6, count any <= 2
  - 4d6 #=5 -- roll 4d6, count any equal to 5
- successes and failures
  - A normal count operation # discards the rolled dice and changes the result to be the count
    - For example, 2d6#<=3 rolls [3,4] then counts which results are <=3 , returning [1]
  - But, sometimes you want to be able to count successes/failures without discarding the dice rolls. In this case, use modifiers #s, #f, #cs, #cf to add metadata to the results.
    - 6d6 #f<=2 #s>=5 #cs6 #cf1 -- roll 6d6, count results <= 2 as failures, >= 5 as successes, =6 as critical successes, =1 as critical failures
      - The above returns a result like: RollSummary(total: 22, results: [6, 2, 1, 5, 3, 5], metadata: {rolled: [6, 2, 1, 5, 3, 5], score: {successes: [6, 5, 5], failures: [2, 1], critSuccesses: [6], critFailures: [1]}})
  - NOTE: order matters
    - 2d20 kh #cf #cs -- roll 2d20, keep the highest, count critical successes & failures. If this rolled [1,18], the 1 is dropped and the result metadata won't record a critical failure. If that's not the behavior you want, move the counts prior to the drop (2d20 #cf #cs kh).
arithmetic operations
- parenthesis to force a certain order of operations
- addition is a little special -- could be a sum of ints, or it can be used to aggregate results of multiple dice rolls
  - Addition of integers is the usual sum
    - 4+5
    - 2d6 + 1
  - Addition of roll results combines the results (use parens to ensure the order of operations is what you desire)
    - (5d6+5d10)-L2 -- roll 5d6 and 5d10, and from aggregate results drop the lowest 2.
    - 5d6+5d10-L2 -- roll 5d6 and 5d10, and from only the 5d10 results drop the lowest 2. equivalent to 5d6+(5d10-L2)
- * for multiplication
- - for subtraction
- numbers must be integers
- division is not supported.

Random Number Generator

By default, Random.secure() is used. You can select other RNGs when creating the dice expression. Random() will be faster than Random.secure(); if you're doing lots of rolls for use cases where security doesn't matter, you will want to use Random().

For example, you might create a dice-rolling app that both provides rolls and displays statistics (mean, stddev, etc) about the dice expression. To do that, you might create two separate DiceExpression objects for the same user-input -- one with the secure RNG (run whenever a user clicks a button), and the second to display min/max/mean/stddev/etc

  final diceExpr_SecureRNG = DiceExpression.create('2d6');
  final diceExpr_FastRNG = DiceExpression.create('2d6', Random());
  
  //....
  // on button-click, roll the dice
  final roll = diceExpr_SecureRNG.roll();
  
  //....
  // when dice expr changes, update the stats graph. 
  final stats = await diceExpr_FastRNG.stats();
  // output of stats: {mean: 6.98, stddev: 2.41, min: 2, max: 12, count: 10000, histogram: {2: 310, 3: 557, 4: 787, 5: 1090, 6: 1450, 7: 1646, 8: 1395, 9: 1147, 10: 825, 11: 526, 12: 267}}

CLI Usage

There's no executable in bin, but there's an example CLI at example/main.dart.

Usage:

❯ dart run example/main.dart -h
Usage:
-n, --num                       Number of times to roll the expression
                                (defaults to "1")
-o, --output                    output type

          [json]                output JSON
          [plain] (default)     output using toString
          [pretty]              output result summary and detailed results of evaluating the expression tree

-r, --random                    Random number generator to use.

          [<integer>]           pseudorandom generator initialized with given seed
          [pseudo] (default)    pseudorandom generator
          [secure]              secure random

-v, --[no-]verbose              Enable verbose logging
-s, --[no-]stats                Output statistics for the given dice expression. Uses n=10000 unless overridden
-h, --[no-]help

Examples:

❯ dart example/main.dart '3d6'
(3d6) ===> RollSummary(total: 13, results: [3, 6, 4], metadata: {rolled: [3, 6, 4]})


# run N number of rolls
❯ dart run example/main.dart -n5 '3d6'
(3d6) ===> RollSummary(total: 10, results: [2, 2, 6], metadata: {rolled: [2, 2, 6]})
(3d6) ===> RollSummary(total: 12, results: [6, 4, 2], metadata: {rolled: [6, 4, 2]})
(3d6) ===> RollSummary(total: 5, results: [2, 1, 2], metadata: {rolled: [2, 1, 2]})
(3d6) ===> RollSummary(total: 10, results: [5, 3, 2], metadata: {rolled: [5, 3, 2]})
(3d6) ===> RollSummary(total: 13, results: [4, 5, 4], metadata: {rolled: [4, 5, 4]})



# show statistics for a dice expression
❯ dart example/main.dart  -s '3d6'
{mean: 10.5, stddev: 2.97, min: 3, max: 18, count: 10000, histogram: {3: 49, 4: 121, 5: 273, 6: 461, 7: 727, 8: 961, 9: 1153, 10: 1182, 11: 1272, 12: 1151, 13: 952, 14: 733, 15: 486, 16: 289, 17: 154, 18: 36}}

Sometimes it's nice to change the output type so you can see the graph of results:

# show the result graph:
❯ dart run example/main.dart -o pretty '3d6 #cs #cf'
(((3d6) #cs ) #cf ) ===> RollSummary(total: 13, results: [1, 6, 6], metadata: {rolled: [1, 6, 6], score: {critSuccesses: [6, 6], critFailures: [1]}})
  (((3d6) #cs ) #cf ) =count=> RollResult(total: 13, results: [1, 6, 6], metadata: {score: {critFailures: [1]}})
      ((3d6) #cs ) =count=> RollResult(total: 13, results: [1, 6, 6], metadata: {score: {critSuccesses: [6, 6]}})
          (3d6) =rollDice=> RollResult(total: 13, results: [1, 6, 6], metadata: {rolled: [1, 6, 6]})


❯ dart run example/main.dart -o json '3d6 #cs #cf'
{"expression":"(((3d6) #cs ) #cf )","total":9,"results":[2,3,4],"detailedResults":{"expression":"(((3d6) #cs ) #cf )","opType":"count","nsides":6,"ndice":3,"results":[2,3,4],"left":{"expression":"((3d6) #cs )","opType":"count","nsides":6,"ndice":3,"results":[2,3,4],"left":{"expression":"(3d6)","opType":"rollDice","nsides":6,"ndice":3,"results":[2,3,4],"metadata":{"rolled":[2,3,4]}}}},"metadata":{"rolled":[2,3,4]}}

Statistics output

I often wonder, "what range of values should I expect?" or "how likely will this roll explode or compound?"

To explore that, you can use stats output:


# roll 4d6
❯ dart run example/main.dart -s '4d6'
{mean: 14.0, stddev: 3.44, min: 4, max: 24, count: 10000, histogram: {4: 5, 5: 28, 6: 72, 7: 163, 8: 280, 9: 468, 10: 573, 11: 816, 12: 948, 13: 1069, 14: 1047, 15: 1118, 16: 1010, 17: 786, 18: 637, 19: 412, 20: 278, 21: 161, 22: 84, 23: 32, 24: 13}}


# roll 4d6 explode 
❯ dart run example/main.dart -s '4d6!'
{mean: 16.7, stddev: 6.46, min: 4, max: 54, count: 10000, histogram: {4: 6, 5: 32, 6: 87, 7: 166, 8: 264, 9: 403, 10: 558, 11: 655, 12: 690, 13: 734, 14: 695, 15: 651, 16: 621, 17: 607, 18: 498, 19: 507, 20: 425, 21: 350, 22: 353, 23: 260, 24: 229, 25: 194, 26: 167, 27: 150, 28: 143, 29: 118, 30: 99, 31: 69, 32: 53

# roll 4d5 compounding 
❯ dart run example/main.dart -s '4d6!!'
{mean: 16.8, stddev: 6.43, min: 4, max: 58, count: 10000, histogram: {4: 6, 5: 29, 6: 78, 7: 162, 8: 230, 9: 389, 10: 506, 11: 635, 12: 726, 13: 705, 14: 751, 15: 682, 16: 597, 17: 602, 18: 571, 19: 498, 20: 456, 21: 365, 22: 310, 23: 286, 24: 262, 25: 192, 26: 167, 27: 156, 28: 114, 29: 92, 30: 76, 31: 72, 32: 57, 33: 41, 34: 32, 35: 31, 36: 20, 37: 15, 38: 16, 39: 10, 40: 12, 41: 8, 42: 10, 43: 4, 44: 8, 45: 5, 46: 4, 47: 2, 48: 1, 49: 2, 50: 3, 51: 2, 53: 1, 58: 1}}

Or, if I wonder, "in those rolls, how many times might I see a roll >=6?". For that case, I can include a count operation

❯ dart run example/main.dart -s '4d6 #>=6'
{mean: 0.664, stddev: 0.75, min: 0, max: 4, count: 10000, histogram: {0: 4871, 1: 3781, 2: 1192, 3: 144, 4: 12}}

❯ dart run example/main.dart -s '4d6! #>=6'
{mean: 0.793, stddev: 0.973, min: 0, max: 7, count: 10000, histogram: {0: 4846, 1: 3213, 2: 1328, 3: 449, 4: 116, 5: 40, 6: 4, 7: 4}}

❯ dart run example/main.dart -s '4d6!! #>=6'
{mean: 0.665, stddev: 0.747, min: 0, max: 4, count: 10000, histogram: {0: 4840, 1: 3845, 2: 1144, 3: 164, 4: 7}}

Reacting to dice rolls in your application

If you're using this package within an app, you probably want to display dice-rolling events to the user.

There's a couple ways for you to act on roll results. Depending on your use-case, one or more will hopefully fit your needs.

Traversing the result graph

Use the 'left' and 'right' fields of each RollResult node to walk the graph. For an example, see simple.dart

When a dice expression is parsed, it creates a binary tree to evaluate the roll.

For example, the expression (3d6 + 3d6!) kh3 means "roll 3d6 and 3d6!, combine results. Keep the 3 highest" and it creates a graph like:

flowchart TD;
    DROP --> ADD;
    ADD --> ROLLB;
    ADD --> EXPLODE;
    EXPLODE --> ROLLA;
    
    DROP(["(3d6 + 3d6!) kh 3"]);
    ADD(["(3d6 + 3d6!)"]);
    ROLLB(["3d6"]);
    EXPLODE(["(3d6)!"]);
    ROLLA(["3d6"]);

When you roll the dice expression, it traverses the tree from the bottom up and rolls dice or performs the requested operations.

flowchart TD
    subgraph dice expr
        DROP --> ADD;
        ADD --> ROLLB;
        ADD --> EXPLODE;
        EXPLODE --> ROLLA;
    end

    subgraph results
        SUMMARY ---|details| DROP_RESULT;
        DROP_RESULT -->|left| ADD_RESULT;
        ADD_RESULT -->|left| ROLLB_RESULT;
        ADD_RESULT -->|right| EXPLODE_RESULT;
        EXPLODE_RESULT -->|left| ROLLA_RESULT;
    end 
    
    ROLLA -.->|#1| ROLLA_RESULT@{ shape: doc, label: "RollResult <br/><br/>results: 2,3,6<br/>rolled:2,3,6" };
    EXPLODE -.->|#2| EXPLODE_RESULT@{ shape: doc, label: "RollResult <br/><br/>results: 2,3,6,4<br/>rolled:4"};
    ROLLB -.->|#3| ROLLB_RESULT@{ shape: doc, label: "RollResult <br/><br/>results: 1,5,2<br/>rolled:1,5,2"};
    ADD -.->|#4| ADD_RESULT@{ shape: doc, label: "RollResult <br/><br/>results: 2,3,6,4,1,5,2"};
    DROP -.->|#5| DROP_RESULT@{ shape: doc, label: "RollResult<br/><br/>results: 6,5,4<br/>discarded: 2,3,1,2"};
    
    DROP(["(3d6 + 3d6!) kh 3"]);
    ADD(["(3d6 + 3d6!)"]);
    ROLLB(["3d6"]);
    EXPLODE(["(3d6)!"]);
    ROLLA(["3d6"]);
    SUMMARY@{ shape: doc, label: "RollSummary<br/><br/>Total: 15 <br/>results:6,5,4<br/><br/>rolled: 2,3,6,4,1,5,2 <br/>discarded: 2,3,1,2" };

Convert RollResult to JSON

  Map<String,dynamic> rollResultAsJson = DiceExpression.create('2d20kh').roll().toJson();

The returned objects will look roughly like:

{
  "expression": "((2d20) kh )",
  "total": 16,
  "results": [
    16
  ],
  "detailedResults": {
    "expression": "((2d20) kh )",
    "opType": "drop",
    "nsides": 20,
    "ndice": 2,
    "results": [
      16
    ],
    "metadata": {
      "discarded": [
        4
      ]
    },
    "left": {
      "expression": "(2d20)",
      "opType": "rollDice",
      "nsides": 20,
      "ndice": 2,
      "results": [
        4,
        16
      ],
      "metadata": {
        "rolled": [
          4,
          16
        ]
      }
    }
  },
  "metadata": {
    "rolled": [
      4,
      16
    ],
    "discarded": [
      4
    ]
  }
}

Listen to RollResult events

You can register one or more listeners that will be informed of roll events. There is a default logging listener that logs at FINE level.


    // if you want to listen to every individual operation within the expression
    DiceExpression.registerListener((rollResult) {
      stdout.writeln('${rollResult.opType.name} -> $rollResult');
    });

    // if you want to listen for the RollSummary
    DiceExpression.registerSummaryListener((rollSummary) {
      stdout.writeln('$rollSummary');
    });

Alternatively, you may not want to know all roll events, and are only interested in the events for your specific roll. In that case, pass an 'onRoll' method to the roll() method

  DiceExpression.create('2d20kh').roll(
    onRoll: (rr) => stdout.writeln('roll - $rr'),
    onSummary: (summary) => stdout.writeln('summary - $summary')
  );

Features and bugs

Please file feature requests and bugs at the issue tracker.

dart_dice_parser

Example

Dice Notation

Examples:

Supported notation

Random Number Generator

CLI Usage

Statistics output

Reacting to dice rolls in your application

Traversing the result graph

Convert RollResult to JSON

Listen to RollResult events

Features and bugs

Libraries

dart_dice_parser package