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/tuturto/deep-sky/ (https://github.com/tuturto/deep-sky/tree/baa0807dd36b61fd02174b17c10013862af4ec18 is situation before lots of Elm related changes that I mentioned in passing in the episode)