HPR2969: Crewing a spaceship in Haskell

Intro

Every spaceship in game needs a crew to operate it. Smaller ships with fewer components require less crew than huge ones with lots of components.

Types

Unit stats lists amount of crew required to operate a spaceship and if they need sleeping quarters.

data UnitStats = UnitStats

    { unitStatsMinimumCrew :: ![CrewRequirement]

    , unitStatsNominalCrew :: ![CrewRequirement]

    , unitStatsCrewSpace :: !TotalCrewSpace

    , unitStatsCrewSpaceRequired :: !CrewSpaceReq

    } deriving (Show, Read, Eq)

Different positions a crew can have is an enumeration:

data CrewPosition =

    Commander

    | Navigator

    | Signaler

    | SensorOperator

    | Gunner

    | Doctor

    | Nurse

    | Driver

    | Helmsman

    | Artificer

    | Crew

    | Passenger

    deriving (Show, Read, Eq, Enum, Bounded)

derivePersistField "CrewPosition"

Rank of a crew member isn’t a military rank, but rather their position in ship’s internal hierarchy:

data CrewRank =

    SecondClass

    | FirstClass

    | Senior

    | Chief

    deriving (Show, Read, Eq, Enum, Bounded)

derivePersistField "CrewRank"

Amount of crew is newtype that helps me not to mix different types of numbers with each other.

newtype CrewAmount = CrewAmount { unCrewAmount :: Int }

    deriving (Show, Read, Eq, Ord, Num)

Total crew space of a ship is divided to three different types: steerage, standard and luxury.

data TotalCrewSpace = TotalCrewSpace

    { totalCrewSpaceSteerage :: !(CrewSpace SteerageQuarters)

    , totalCrewSpaceStandard :: !(CrewSpace StandardQuarters)

    , totalCrewSpaceLuxury :: !(CrewSpace LuxuryQuarters)

    } deriving (Show, Read, Eq)

Again, crew space is newtype so I don’t mix different types of numbers with each other.

data CrewSpace a =

    CrewSpace { unCrewSpace :: CrewAmount }

    deriving (Show, Read, Eq)

I could have modeled fact that vehicle might need crew space with Bool, but having a descriptive name and type is more to my liking.

data CrewSpaceReq =

    CrewSpaceRequired

    | CrewSpaceOptional

    deriving (Show, Read, Eq)

derivePersistField "CrewSpaceReq"

The fact that single person could manage multiple components is reflected by ComponentCrewReq having Double instead of Integer

-- | Crew requirements for a component

data ComponentCrewReq =

    ComponentCrewReq CrewPosition Double

    deriving (Show, Read, Eq)

In closing

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