diceprob

Go package for calculating combinations and probabilities for complex dice expressions.

Purpose

diceprob is a personal combinatorics and game design hobby turned into Golang package.

For decades I've been fascinated with game design and specifically dice as the randomizer element of those designs.

I spent years researching combinatorics and probabilities of dice as a personal hobby. Maybe that's weird. This package is based on prior work I've done on a Perl module Games::Dice::Probability. I'm updating it to be Golang and useful to me now.

The Math

There's a lot of math behind the scenes. I discuss it on my website.

Install

Install with:

go get github.com/jason-dour/diceprob

Dice Expression Syntax

• N
  • The number of dice in a single dice roll.
  • Can be any integer number.
• S
  • The number of sides on the dice in a single dice roll.
  • Can be any integer number, as well as F or f for Fudge/FATE dice.
• NdS
  • Roll N dice, each with same number of sides S.
  • Examples:
    • 1d6
    • 3d6
    • 1d4
    • 1d20
    • 3df
• midS
  • Roll 3 dice, each with same number of sides S, and return the middle value of the three values.
  • Examples:
    • mid20
    • mid10
    • midf
• [+ | - | * | /]
  • Math operators; will add/subtract/multiply/divide the left and right terms.
  • Example:
    • 2d6+1d4
• [0-9+]
  • Modifier; a fixed number.
  • Example:
    • 2d6+1
    • 3d6-4
• ( expression )
  • Grouping; you may use parentheses to enclose sub-expressions, to ensure proper calculation.
  • Example:
    • (1d6+2)*3

Usage

Everything is driven through the DiceProb type, and its methods.

Create a new instance by providing your dice expression:

d, err := diceprob.New("3d6")
if err != nil {
  panic(err)
}

Creating the instance will automatically parse the expression into an object tree.

repr.Println(d.ParsedExpression())

&diceprob.Expression{
  Left: &diceprob.Term{
    Left: &diceprob.Atom{
      RollExpr: &diceprob.DiceRoll("3d6"),
    },
  },
}

From there you can calculate the outcomes, distribution, probabilities, et al.

d.Calculate()

And call them for display or computation.

fmt.Printf("Expression: %s\n", d.InputExpression())
fmt.Printf("Bounds: %v..%v\n", d.Min(), d.Max())
fmt.Printf("Permutations: %v\n", d.Permutations())
fmt.Printf("Outcome Set: %s\n", strings.Join(*d.OutcomesString(), ","))
fmt.Printf("Distribution:\n  Outcome | Frequency | Probability\n")

for _, i := range *d.Outcomes() {
  fmt.Printf("  %-8d  %-8d    %.6g\n", i, (*d.Distribution())[i], (*d.Probabilities())[i])
}

Or you can just "roll" the dice expression and retrieve a value.

d.Roll()

Notes

• Memoize for speed?
  • "golang.org/x/tools/internal/memoize"