# Dice Roller & Parser

This dice roller is a string parser that returns an object containing the component parts of the dice roll. It supports the full [Roll20 Dice Specification](https://roll20.zendesk.com/hc/en-us/articles/360037773133-Dice-Reference#DiceReference-Roll20DiceSpecification). It uses a [pegjs](https://github.com/pegjs/pegjs) grammar to create a [representation of the dice roll format](#parsed-roll-output). This can then be converted into a simple number value, or to a [complex object](#roll-result-output) used to display the full roll details.

## Quickstart

Install the library using:

```bash
npm install dice-roller-parser
```

Once installed, simply load the library, either in the browser:

```html
<script src="node_modules/dice-roller-parser/dist/index.js"></script>
```

Or in node:

```javascript
import { DiceRoller } from "dice-roller-parser";
```

Then create a new instance of the [`DiceRoller`](#DiceRoller) class, and use it to perform some dice rolls.

```javascript
const diceRoller = new DiceRoller();

//	Returns the total rolled value
const roll = diceRoller.rollValue("2d20kh1");
console.log(roll);

//	Returns an object representing the dice roll, use to display the component parts of the roll
const rollObject = diceRoller.roll("2d20kh1");
console.log(rollObject.value);
```

## Usage

This library exposes two classes, a [`DiceRoller`](#DiceRoller) and a [`DiscordRollRenderer`](#DiscordRollRenderer).

### `DiceRoller`

The `DiceRoller` class manages parsing of a dice string and performing rolls based upon the result.

```javascript
//	Creates a new instance of the DiceRoller class
const roller = new DiceRoller();
```

#### Constructor options

The default constructor uses `Math.random` and applies a maximum number of rolls per die of 1000. These can be specified using the following constructor overloads.

##### `DiceRoller(GeneratorFunction)`

You can specify a function to be used as the random number generator by the dice roller. This function should be of the type `() => number` and return a number between 0 and 1. By default, it uses the built-in `Math.random` method.

```javascript
//	Default constructor using Math.random
const roller = new DiceRoller();

//	Uses a custom random generator that always returns 0.5
const roller = new DiceRoller(() => 0.5);
```

This can be read or modified using the `randFunction` property.

```javascript
roller.randFunction = () => 0.5;
```

##### `DiceRoller(GeneratorFunction, MaxRollsPerDie)`

To prevent attempting to parse very large numbers of die rolls, a maximum number of rolls for a die can be specified. The default value is set to 1000.

```javascript
//	Uses the default constructor with a limit of 100 rolls per die
const roller = new DiceRoller(null, 100);

//	Uses a custom random generator that always returns 0.5, and a limit of 10 rolls per die
const roller = new DiceRoller(() => 0.5, 10);
```

This can be read or modified using the `maxRollCount` property.

```javascript
roller.maxRollCount = 75;
```

#### Class Usage

Once the `DiceRoller` class has been constructed, there are three options for performing a dice roll:

-   Getting a roll result directly
-   Generate an object to represent the dice roll
-   Just parse the input and add your own rolling logic

##### Getting a direct roll result

The `rollValue` method takes a dice string input, parses it, performs a roll and returns the calculated number value result.

```javascript
//	Rolls 2 d20 dice and keeps the value of the highest
const roll = roller.rollValue("2d20kh1");

//	Prints out the numeric value result
console.log(roll);
```

##### Generate an object representing the dice roll

The `roll` method takes a dice string input, parses it, performs a roll and then returns an object that represents the roll. Using the roll objects, you can build your own roll display functionality, rather than just outputting the final value.

```javascript
//	Rolls 2 d20 dice and keeps the value of the highest
const roll = roller.roll("2d20kh1");

//	Print out the full roll breakdown
printDiceRoll(roll);
//	Prints out the numeric value result
console.log(`Final roll value: ${roll.Value}`);
```

See the [roll result output](#roll-result-output) in the [output types](#output-types) section below for more details on the returned object.

##### Just parse the value

The `parse` method takes a dice string input, parses it and returns a representation of the parsed input. This can either be used to perform a dice roll or re-construct the original input. The `rollParsed` method takes this parsed result as an input, performs the roll and returns the same output as from the [`roll`](#generate-an-object-representing-the-dice-roll) method.

```javascript
//	Rolls 2 d20 dice and keeps the value of the highest
const parsedInput = roller.parse("2d20kh1");

//	Print out a re-constructed input string
printParsedInput(parsedInput);

//	Run the roller on the parsed object
const roll = roller.rollParsed(parsedInput);

//	Print out the full roll breakdown
printDiceRoll(roll);
//	Print out the numeric value result
console.log(`Final roll value: ${roll.Value}`);
```

See the [parsed roll output](#parsed-roll-output) in the [output types](#output-types) section below for more details on the returned object.

### `DiscordRollRenderer`

The `DiscordRollRenderer` class is an example renderer class that takes a rolled input represented by a [`RollBase`](#RollBase) object and renders it to a string in a markdown format, compatible with Discord.

```javascript
//	Creates a new instance of the DiceRoller class
const renderer = new DiscordRollRenderer();
```

#### Class Usage

The `DiscordRollRenderer` exposes a single `render` method with a single parameter, the [`RollBase`](#RollBase) object to render, and returns the rendered string.

```javascript
//	Rolls 2 d20 dice and keeps the value of the highest
const roll = roller.rollValue("2d20kh1");

//	Get the formatted string
const render = renderer.render(roll);
console.log(render);
```

## Development

To develop this library, simply clone the repository, run an install:

```bash
npm install
```

Then do a build:

```bash
npm run build
```

This does four things:

```bash
# Clean any existing builds
npm run clean

# Build the dice grammer
npx pegjs src/diceroll.pegjs

# Run tslint against the project
tslint -c tslint.json --project tsconfig.json

# Then run webpack to build and package everything up nicely
webpack
```

To run the test suite, use:

```bash
npm run test
```

That's all there is to it!

## Output Types

The following object types are output from the [`DiceRoller`](#DiceRoller) class, and are available as interfaces for typescript users.

### Roll Result Output

The object returned by a roll result is made up of the following types.

#### `RollBase`

The base class for all die rolls, extended based upon the type property.

| Property | Type                    | Description                                                         |
| -------- | ----------------------- | ------------------------------------------------------------------- |
| success  | `boolean`               | Was the roll a success, for target number rolls. Example: `3d6 > 3` |
| type     | [`RollType`](#RollType) | The type of roll that this object represents.                       |
| valid    | `boolean`               | Is the roll still valid, and included in calculations.              |
| value    | `number`                | The rolled or calculated value of this roll.                        |
| label    | `string`                | The display label for this roll. This property is optional.         |
| order    | `number`                | A property used to maintain ordering of dice rolls within groups.   |

#### `RollType`

An enum of the valid types of roll. The possible values are:

-   `"number"`
-   [`"diceexpressionroll"`](#DiceExpressionRoll)
-   [`"expressionroll"`](#ExpressionRoll)
-   [`"mathfunction"`](#MathFunctionRoll)
-   [`"grouproll"`](#GroupRoll)
-   `"fate"`
-   [`"die"`](#DiceRollResult)
-   [`"roll"`](#DieRoll)
-   [`"fateroll"`](#FateDieRoll)

#### `GroupedRoll`

An intermediate interface extended for groups of dice. This interface extends [`RollBase`](#RollBase).

| Property | Type                               | Description                               |
| -------- | ---------------------------------- | ----------------------------------------- |
| dice     | `Array<`[`RollBase`](#RollBase)`>` | The rolls included as part of this group. |

#### `DiceExpressionRoll`

A representation of a dice expression. This interface extends [`GroupedRoll`](#GroupedRoll).

**Example**

> `2d20 + 6d6`

| Property | Type                                                           | Description                                   |
| -------- | -------------------------------------------------------------- | --------------------------------------------- |
| type     | `"diceexpressionroll"`                                         | The type of roll that this object represents. |
| ops      | `Array<`[`DiceGroupMathOperation`](#DiceGroupMathOperation)`>` | The operations to perform on the rolls.       |

#### `ExpressionRoll`

A representation of a mathematic expression. This interface extends [`GroupedRoll`](#GroupedRoll).

**Example**

> `20 * 17`

| Property | Type                                         | Description                                   |
| -------- | -------------------------------------------- | --------------------------------------------- |
| type     | `"expressionroll"`                           | The type of roll that this object represents. |
| ops      | `Array<`[`MathOperation`](#MathOperation)`>` | The operations to perform on the rolls.       |

#### `MathFunctionRoll`

A representation of a mathematic function. This interface extends [`RollBase`](#RollBase).

**Example**

> `floor(20 / 17)`

| Property | Type                            | Description                                       |
| -------- | ------------------------------- | ------------------------------------------------- |
| type     | `"expressionfunc"`              | The type of roll that this object represents.     |
| op       | [`MathFunction`](#MathFunction) | The operations to perform on the rolls.           |
| expr     | [`RollBase`](#RollBase)         | The expression that the function is applied upon. |

#### `GroupRoll`

A representation of a group of rolls

**Example**

> {4d6,3d6}. This interface extends [`GroupedRoll`](#GroupedRoll).

| Property | Type          | Description                                   |
| -------- | ------------- | --------------------------------------------- |
| type     | `"grouproll"` | The type of roll that this object represents. |

#### `DiceRollResult`

The rolled result of a group of dice. This interface extends [`RollBase`](#RollBase).

**Example**

> `6d20`

| Property | Type                            | Description                                   |
| -------- | ------------------------------- | --------------------------------------------- |
| die      | [`RollBase`](#RollBase)         | The die this result represents.               |
| type     | `"die"`                         | The type of roll that this object represents. |
| rolls    | [`DieRollBase`](#DieRollBase)[] | Each roll of the die.                         |
| count    | [`RollBase`](#RollBase)         | The number of rolls of the die.               |
| matched  | `boolean`                       | Whether this is a match result.               |

#### `DieRollBase`

An intermediate interface extended for individual die rolls (see below). This interface extends [`RollBase`](#RollBase).

| Property | Type      | Description                   |
| -------- | --------- | ----------------------------- |
| roll     | `number`  | The rolled result of the die. |
| matched  | `boolean` | Whether this roll is a match. |

#### `DieRoll`

A roll on a regular die. This interface extends [`DieRollBase`](#DieRollBase).

**Example**

> `d20`

| Property | Type                            | Description                                                    |
| -------- | ------------------------------- | -------------------------------------------------------------- |
| die      | `number`                        | The die number to be rolled.                                   |
| type     | `"roll"`                        | The type of roll that this object represents.                  |
| critical | [`CriticalType`](#CriticalType) | If this role is a critical success or failure (for rendering). |

#### `FateDieRoll`

A roll on a fate die. This interface extends [`DieRollBase`](#DieRollBase).

**Example**

> `dF`

| Property | Type         | Description                                   |
| -------- | ------------ | --------------------------------------------- |
| type     | `"fateroll"` | The type of roll that this object represents. |

### Parsed Roll Output

The following interfaces are exposed by the library as a reresentation of the parsed input string. The response from the `parse` method is a `RootType` object and could be any of the interfaces that extend it.

#### `ParsedObjectType`

An enum of the valid types of roll. The possible values are:

-   [`"number"`](#NumberType)
-   [`"inline"`](#InlineExpression)
-   [`"success"`](#SuccessFailureCritModType)
-   [`"failure"`](#SuccessFailureCritModType)
-   [`"crit"`](#SuccessFailureCritModType)
-   [`"critfail"`](#SuccessFailureCritModType)
-   [`"match"`](#MatchModType)
-   [`"keep"`](#KeepDropModType)
-   [`"drop"`](#KeepDropModType)
-   [`"group"`](#GroupedRoll)
-   [`"diceExpression"`](#RollExpressionType)
-   [`"sort"`](#SortRollType)
-   [`"explode"`](#ReRollMod)
-   [`"compound"`](#ReRollMod)
-   [`"penetrate"`](#ReRollMod)
-   [`"reroll"`](#ReRollMod)
-   [`"rerollOnce"`](#ReRollMod)
-   [`"target"`](#TargetMod)
-   [`"die"`](#DiceRoll)
-   [`"fate"`](#FateExpr)
-   [`"expression"`](#MathExpression)
-   [`"math"`](#MathType)
-   [`"mathfunction"`](#MathFunctionExpression)

#### `ParsedType`

This is the base interface for all parsed types.

| Property | Type     | Description                                     |
| -------- | -------- | ----------------------------------------------- |
| type     | `string` | The type of parsed item this object represents. |

#### `RootType`

This is the base interface for a subset of parsed types, only those that can be the root type. This object extends the [`ParsedType`](#ParsedType) interface.

| Property | Type      | Description                                                       |
| -------- | --------- | ----------------------------------------------------------------- |
| label?   | `string`  | The text label attached to this roll. This property is optional.  |
| root     | `boolean` | A boolean flag to indicate if this is the root of the parse tree. |

#### `NumberType`

This object represents a single number in the input. This object extends the [`RootType`](#RootType) interface.

| Property | Type       | Description                                     |
| -------- | ---------- | ----------------------------------------------- |
| type     | `"number"` | The type of parsed item this object represents. |
| value    | `number`   | The value of the number.                        |

#### `InlineExpression`

This object represents an inline dice expression within a string, wrapped in double square brackets. This object extends the [`RootType`](#RootType) interface.

**Example**

> `I want to roll [[2d20]] dice`

| Property | Type                        | Description                                          |
| -------- | --------------------------- | ---------------------------------------------------- |
| type     | `"inline"`                  | The type of parsed item this object represents.      |
| expr     | [`Expression`](#Expression) | The expression that was parsed as the inline string. |

#### `AnyRoll`

A combined type representing any valid roll. This is a combination of the following types:

-   [`GroupedRoll`](#GroupedRoll)
-   [`FullRoll`](#FullRoll)
-   [`NumberType`](#NumberType)

#### `ModGroupedRoll`

This object represents a grouped roll with an optional modifier. This object extends the [`RootType`](#RootType) interface.

**Example**

> `{4d6+3d8}kh1`

| Property | Type                                                                                                 | Description                                      |
| -------- | ---------------------------------------------------------------------------------------------------- | ------------------------------------------------ |
| mods     | `Array<`[`KeepDropModType`](#KeepDropModType)`,`[`SuccessFailureModType`](#SuccessFailureModType)`>` | The modifiers to be applied to the grouped roll. |

#### `SuccessFailureCritModType`

An object representing a success test modifier. This object extends the [`ParsedType`](#ParsedType) interface.
A `"success"` or `"failure"` modifier converts the result into a success type result which returns the number of rolls that meet the target.
A `"crit"` or `"critfail"` modifier tests the roll for whether or not the roll should be displayed as a critical success or critical failure.

**Example**

> Success: `3d6>3`
> Failure: `3d6f<3`

| Property | Type                                       | Description                                       |
| -------- | ------------------------------------------ | ------------------------------------------------- |
| type     | `"success", "failure", "crit", "critfail"` | The type of parsed item this object represents.   |
| mod      | [`CompareOperation`](#CompareOperation)    | The check type to use for the condition.          |
| expr     | [`RollExpression`](#RollExpression)        | An expression representing the success condition. |

#### `SuccessFailureModType`

Equivalent to the [`SuccessFailureCritModType`](#SuccessFailureCritModType) but only supporting "success" and "failure" modifiers. This object extends the [`SuccessFailureCritModType`](#SuccessFailureCritModType) interface.

**Example**

> Success: `3d6>3`
> Failure: `3d6f<3`

| Property | Type                                    | Description                                       |
| -------- | --------------------------------------- | ------------------------------------------------- |
| type     | `"success", "failure"`                  | The type of parsed item this object represents.   |
| mod      | [`CompareOperation`](#CompareOperation) | The check type to use for the condition.          |
| expr     | [`RollExpression`](#RollExpression)     | An expression representing the success condition. |

#### `MatchModType`

An object representing a match type modifier, used to modify the display of dice output in roll20. This object extends the [`ParsedType`](#ParsedType) interface.

**Example**

> `2d6m`

When used with the `mt` extension, will return the number of matches found.

**Example**

> `20d6mt`

Additional arguments can be specified that increase the required number of matches or to add a constraint to matches.

**Example**

> `20d6mt3 counts matches of 3 items`

**Example**

> `20d6m>3 Only counts matches where the rolled value is > 3`

| Property | Type                                    | Description                                                                                            |
| -------- | --------------------------------------- | ------------------------------------------------------------------------------------------------------ |
| type     | `"match"`                               | The type of parsed item this object represents.                                                        |
| min      | [`NumberType`](#NumberType)             | The minimum number of matches to accept. This property defaults to 2 as a [`NumberType`](#NumberType). |
| count    | `boolean`                               | Whether or not to count the matches.                                                                   |
| mod?     | [`CompareOperation`](#CompareOperation) | The check type to use for the match condition, if specified. This field is optional.                   |
| expr?    | [`RollExpression`](#RollExpression)     | An expression representing the match condition, if specified. This field is optional.                  |

#### `KeepDropModType`

An object representing a keep or drop modifier, specifying a number of dice rolls to keep or drop, either the highest or lowest rolls. This object extends the [`ParsedType`](#ParsedType) interface.

**Example**

> Keep: `2d20kh1`
> Drop: `2d20dl1`

| Property | Type                                | Description                                                                                                                               |
| -------- | ----------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------- |
| type     | `"keep", "drop"`                    | The type of parsed item this object represents.                                                                                           |
| highlow  | [`HighLowType`](#HighLowType)       | Whether to keep/drop the highest or lowest roll.                                                                                          |
| expr     | [`RollExpression`](#RollExpression) | An expression representing the number of rolls to keep/drop. This property defaults to 1 as a [`NumberType`](#NumberType). Example: `2d6` |

#### `GroupedRoll`

This object represents a group of rolls combined, with optional modifiers. This object extends the [`ModGroupedRoll`](#ModGroupedRoll) interface.

**Example**

> `{2d6,3d6}`

| Property | Type                                           | Description                                     |
| -------- | ---------------------------------------------- | ----------------------------------------------- |
| type     | `"group"`                                      | The type of parsed item this object represents. |
| rolls    | `Array<`[`RollExpression`](#RollExpression)`>` | The group of rolls included in this group.      |

#### `RollExpressionType`

An object representing a roll expression including complex rolls and groups, only allows addition operations. This object extends the [`RootType`](#RootType) interface.

**Example**

> `{2d6,3d6}kh1 + {3d6 + 2d6}kh2`

| Property | Type                                                                                                                                | Description                                                |
| -------- | ----------------------------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------- |
| head     | [`RollOrExpression`](#RollOrExpression)                                                                                             | The initial roll or expression for the roll expression.    |
| type     | `"diceExpression"`                                                                                                                  | The type of parsed item this object represents.            |
| ops      | `Array<`[`MathType`](#MathType)`<`[`RollOrExpression`](#RollOrExpression)`,`[`DiceGroupMathOperation`](#DiceGroupMathOperation)`>>` | The operations to apply to the initial roll or expression. |

#### `RollExpression`

A helper type combination of a complex roll expression, a roll, or a math expression. Represents the following types:

-   [`RollExpressionType`](#RollExpressionType)
-   [`RollOrExpression`](#RollOrExpression)

#### `RollOrExpression`

A helper type combination of a roll, or a math expression. Represents the following types:

-   [`FullRoll`](#FullRoll)
-   [`Expression`](#Expression)

#### `FullRoll`

An object representing a roll including the dice roll, and any modifiers. This object extends the [`DiceRoll`](#DiceRoll) interface.

**Example**

> `2d6kh1`

| Property | Type                                                                         | Description                                                             |
| -------- | ---------------------------------------------------------------------------- | ----------------------------------------------------------------------- |
| mods?    | `Array<`[`ReRollMod`](#ReRollMod)`,`[`KeepDropModType`](#KeepDropModType)`>` | Any modifiers attached to the roll. This property is optional.          |
| targets? | `Array<`[`SuccessFailureCritModType`](#SuccessFailureCritModType)`>`         | Any success or failure targets for the roll. This property is optional. |
| match?   | [`MatchModTyp`](#MatchModTyp)                                                | Any match modifiers for the roll. This property is optional.            |
| sort?    | [`SortRollType`](#SortRollType)                                              | Any sort operations to apply to the roll. This property is optional.    |

#### `SortRollType`

A sort operation to apply to a roll. This object extends the [`ParsedType`](#ParsedType) interface.

**Example**

> `10d6sa`

| Property | Type      | Description                                     |
| -------- | --------- | ----------------------------------------------- |
| type     | `"sort"`  | The type of parsed item this object represents. |
| asc      | `boolean` | Whether to sort ascending or descending.        |

#### `ReRollMod`

An object representing a re-roll operation to apply to a roll. Can be one of the following types:

-   `"explode"`: re-rolls any dice that meet the target, continuing if the new roll matches
-   `"compound"`: re-rolls any dice that meet the target, continuing if the new roll matches and adding the results into a single roll
-   `"penetrate"`: re-rolls any dice that meet the target subtracting 1 from the new value, continuing if the new roll matches
-   `"reroll"`: re-rolls a die as long as it meets the target, keeping the final roll
-   `"rerollOnce"`: re-rolls a die once if it meets the target, keeping the new roll

**Example**

> `2d6!`

| Property | Type                                                         | Description                                            |
| -------- | ------------------------------------------------------------ | ------------------------------------------------------ |
| type     | `"explode", "compound", "penetrate", "reroll", "rerollOnce"` | The type of parsed item this object represents.        |
| target   | [`TargetMod`](#TargetMod)                                    | The target modifier to compare the roll value against. |

#### `TargetMod`

An object represting a target modifier to apply to a roll. This object extends the [`ParsedType`](#ParsedType) interface.

| Property | Type                                    | Description                                            |
| -------- | --------------------------------------- | ------------------------------------------------------ |
| type     | `"target"`                              | The type of parsed item this object represents.        |
| mod      | [`CompareOperation`](#CompareOperation) | The check type to use for the condition.               |
| value    | [`RollExpr`](#RollExpr)                 | An expression representing the target condition value. |

#### `DiceRoll`

The representation of a die roll. This object extends the [`RootType`](#RootType) interface.

**Example**

> `2d6`

| Property | Type                                              | Description                                                                              |
| -------- | ------------------------------------------------- | ---------------------------------------------------------------------------------------- |
| die      | [`RollExpr`](#RollExpr)`,`[`FateExpr`](#FateExpr) | The die value to roll against, can be a fate die, a number or a complex roll expression. |
| count    | [`RollExpr`](#RollExpr)                           | The number of time to roll this die.                                                     |
| type     | `"die"`                                           | The type of parsed item this object represents.                                          |

#### `FateExpr`

The representation of a fate die roll. This object extends the [`ParsedType`](#ParsedType) interface.

**Example**

> `2dF`

| Property | Type     | Description                                     |
| -------- | -------- | ----------------------------------------------- |
| type     | `"fate"` | The type of parsed item this object represents. |

#### `RollExpr`

A helper type combination of a number or value that is not an expression. Represents the following types:

-   [`MathExpression`](#MathExpression)
-   [`NumberType`](#NumberType)

#### `Expression`

A helper type combination of expression types. Represents the following types:

-   [`InlineExpression`](#InlineExpression)
-   [`MathExpression`](#MathExpression)

#### `MathExpression`

A math type expression between two or more dice rolls. This object extends the [`RootType`](#RootType) interface.

**Example**

> `2d6 + 3d6 * 4d6`

| Property | Type                                                        | Description                                     |
| -------- | ----------------------------------------------------------- | ----------------------------------------------- |
| head     | [`AnyRoll`](#AnyRoll)                                       | The initial roll to perform operations against. |
| type     | `"expression"`                                              | The type of parsed item this object represents. |
| ops      | `Array<`[`MathType`](#MathType)`<`[`AnyRoll`](#AnyRoll)`>>` | The operations to apply to the initial roll.    |

#### `MathType`

An object representating an roll math operation to be applied and the value to apply it to. This object extends the [`ParsedType`](#ParsedType) interface.
The interface for this object takes a templated type `TailType` which specifies the type of the second value used in the operation.
There is a second templated type `OpValues` which specifies the type of operations that can be used. This defaults to `Array<`[`MathOperation`](#MathOperation)>`.

**Example**

> `+ 3d6 (as part of 2d6 + 3d6)`

| Property | Type       | Description                                     |
| -------- | ---------- | ----------------------------------------------- |
| type     | `"math"`   | The type of parsed item this object represents. |
| op       | `OpValues` | The math operation to perform.                  |
| tail     | `TailType` | The second value to use in the operation.       |

#### `MathFunctionExpression`

An object representing a math function to be applied and the expression to apply it to. This object extends the [`RootType`](#RootType) interface.

**Example**

> `floor(3d6 / 2d4)`

| Property | Type                            | Description                                     |
| -------- | ------------------------------- | ----------------------------------------------- |
| type     | `"mathfunction"`                | The type of parsed item this object represents. |
| op       | [`MathFunction`](#MathFunction) | The function to be applied.                     |
| expr     | [`AnyRoll`](#AnyRoll)           | The expression to apply the function on.        |

### Helper Types

The following are support types used by the above interfaces.

#### `DiceGroupMathOperation`

A helper type representing the valid operations for a math operation on a group of dice.

> `"+" | "-"`

#### `MathOperation`

A helper type representing the valid operations for a math operation.

> `"+" | "-" | "*" | "/" | "%" | "**"`

#### `MathFunction`

A helper type representing the valid operations for a math operation.

> `"floor" | "ceil" | "round" | "abs"`

#### `CriticalType`

A helper type used when marking a roll as a critical success or failure.

> `"success" | "failure" | null`

#### `CompareOperation`

A helper type for the available operations for a comparison point.

> `">" | "<" | "="`

#### `HighLowType`

A helper type used to determine which rolls to keep or drop.

> `"h" | "l" | null`