Data.Voting.BordaCount

Implementation of the modified Borda count election method.

The implementation implements the modified Borda count election method, optionally with different weights for different participants.

See https://en.wikipedia.org/wiki/Borda_count.

The election runs in two phases. First individual Votes on options from a certain participant are gathered and ranked into the participant's Ballot using the function ballot.

Then all ballots are gathered and an election is held, resulting in a list of election Results, one for each option.

Except for the Vote data constructor, you should not use other data constructors, as they do not reflect invariants correctly. However, the ballot and election will enforce variants.

Voting

data Vote o

A vote is an attribution of a number of points to an option

Constructors

Vote

Fields

• voteRanking :: Int
• voteOption :: o

Instances

Eq o => Eq (Vote o)

Methods

(==) :: Vote o -> Vote o -> Bool

(/=) :: Vote o -> Vote o -> Bool

Show o => Show (Vote o)

Methods

showsPrec :: Int -> Vote o -> ShowS

show :: Vote o -> String

showList :: [Vote o] -> ShowS

data Ballot p o

A ballot with options of type o filled in by a participant of type p.

Constructors

Ballot

Fields

• ballotParticipant :: p
• ballotVotes :: [Vote o]

Instances

(Eq o, Eq p) => Eq (Ballot p o)

Methods

(==) :: Ballot p o -> Ballot p o -> Bool

(/=) :: Ballot p o -> Ballot p o -> Bool

(Show o, Show p) => Show (Ballot p o)

Methods

showsPrec :: Int -> Ballot p o -> ShowS

show :: Ballot p o -> String

showList :: [Ballot p o] -> ShowS

data BallotError o

Errors that can occur when creating a Ballot using ballot.

Constructors

DuplicateRanking o o

The given options have the same ranking

DuplicateOption o

The given option was voted on twice.

Instances

Eq o => Eq (BallotError o)

Methods

(==) :: BallotError o -> BallotError o -> Bool

(/=) :: BallotError o -> BallotError o -> Bool

Show o => Show (BallotError o)

Methods

showsPrec :: Int -> BallotError o -> ShowS

show :: BallotError o -> String

showList :: [BallotError o] -> ShowS

ballot :: Eq o => p -> [Vote o] -> Either (BallotError o) (Ballot p o)

Construct a new ballot for a participant from a collection of votes.

This function constructs a valid ballot or returns an error if the collection of votes is invalid.

Election

data Result o

Result of a certain option of type o of an election.

Constructors

Result o Score Zeros

Instances

Eq o => Eq (Result o)

Methods

(==) :: Result o -> Result o -> Bool

(/=) :: Result o -> Result o -> Bool

Show o => Show (Result o)

Methods

showsPrec :: Int -> Result o -> ShowS

show :: Result o -> String

showList :: [Result o] -> ShowS

newtype Score

The weighted score of a Result.

Constructors

Score Double

Instances

Eq Score

Methods

(==) :: Score -> Score -> Bool

(/=) :: Score -> Score -> Bool

Num Score

Methods

(+) :: Score -> Score -> Score

(-) :: Score -> Score -> Score

(*) :: Score -> Score -> Score

negate :: Score -> Score

abs :: Score -> Score

signum :: Score -> Score

fromInteger :: Integer -> Score

Ord Score

Methods

compare :: Score -> Score -> Ordering

(<) :: Score -> Score -> Bool

(<=) :: Score -> Score -> Bool

(>) :: Score -> Score -> Bool

(>=) :: Score -> Score -> Bool

max :: Score -> Score -> Score

min :: Score -> Score -> Score

Real Score

Methods

toRational :: Score -> Rational

Show Score

Methods

showsPrec :: Int -> Score -> ShowS

show :: Score -> String

showList :: [Score] -> ShowS

newtype Zeros

The number of weighted zeros a Result got.

Constructors

Zeros Double

Instances

Eq Zeros

Methods

(==) :: Zeros -> Zeros -> Bool

(/=) :: Zeros -> Zeros -> Bool

Num Zeros

Methods

(+) :: Zeros -> Zeros -> Zeros

(-) :: Zeros -> Zeros -> Zeros

(*) :: Zeros -> Zeros -> Zeros

negate :: Zeros -> Zeros

abs :: Zeros -> Zeros

signum :: Zeros -> Zeros

fromInteger :: Integer -> Zeros

Ord Zeros

Methods

compare :: Zeros -> Zeros -> Ordering

(<) :: Zeros -> Zeros -> Bool

(<=) :: Zeros -> Zeros -> Bool

(>) :: Zeros -> Zeros -> Bool

(>=) :: Zeros -> Zeros -> Bool

max :: Zeros -> Zeros -> Zeros

min :: Zeros -> Zeros -> Zeros

Real Zeros

Methods

toRational :: Zeros -> Rational

Show Zeros

Methods

showsPrec :: Int -> Zeros -> ShowS

show :: Zeros -> String

showList :: [Zeros] -> ShowS

newtype ElectionError p

Error that can occur when holding an election.

Constructors

DuplicateParticipant p

The given participant voted twice.

Instances

Eq p => Eq (ElectionError p)

Methods

(==) :: ElectionError p -> ElectionError p -> Bool

(/=) :: ElectionError p -> ElectionError p -> Bool

Show p => Show (ElectionError p)

Methods

showsPrec :: Int -> ElectionError p -> ShowS

show :: ElectionError p -> String

showList :: [ElectionError p] -> ShowS

election

Arguments

:: (Eq p, Ord o)

=> (p -> Double)

Weighing function for participants.

-> [Ballot p o]

All ballots.

-> Either (ElectionError p) [Result o]

Election result

Hold an election, collect all the ballots and produce the Result.

This functions assumes that the Ballots are well formed, as returned by the function ballot.

Thee function holds the election, and might return an ElectionError on any irregularity.

election'

Arguments

:: (Eq p, Ord o)

=> [Ballot p o]

All ballots

-> Either (ElectionError p) [Result o]

Election result

Hold an election, but with a weight of 1 for all participants.

See election for more information.

Internal

findFirstDuplicateBy :: (a -> a -> Bool) -> [a] -> Maybe (a, a)

Find the first duplicates, filtered by a function.