HPR2693: Getting started with web based game in Haskell and Elm

Haskell Stack: https://docs.haskellstack.org/en/stable/README/

Stack is a build tool for Haskell with focus on reproducible build plans, multi-package projects, and a consistent, easy-to-learn interface. With stack, one can create new project: stack new my-project yesod-sqlite (more in the quick start guide: https://www.yesodweb.com/page/quickstart)

models is used to define shape of the data and Yesod uses it to generate datatypes and database for you. For example, to define a Star that has name, spectral type, luminosity class and link to StarSystem, one can write:

Star json
    name Text
    starSystemId StarSystemId
    spectralType SpectralType
    luminosityClass LuminosityClass

Custom types, like LuminosityClass, need mapping between datatype and database. In simple cases like this, Yesod can do that:

data LuminosityClass = Iap | Ia | Iab | Ib | II | III | IV | V | VI | VII
    deriving (Show, Read, Eq)
derivePersistField "LuminosityClass"

The "derivePersistField" part is template haskell call that will generate mapping needed.

For those interested seeing some code, source is available at https://github.com/Tuula/deep-sky/ (https://github.com/Tuula/deep-sky/tree/baa0807dd36b61fd02174b17c10013862af4ec18 is situation before lots of Elm related changes that I mentioned in passing in the episode)

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