purecript-crud-1

Main.purs

module Main where

import Prelude
import Control.Monad.Free
import Data.Exists
import Data.Foldable (fold)
import Data.Maybe
import Data.Symbol
import TryPureScript

prog5 = do
  pid <- createPerson $ Person { id: Nothing, name: "Erik", year: 1979 }
  cid <- createCompany $ Company { id: Nothing, ownerId: pid, name: "Shinsetsu" }
  pure pid

------------------------------------------------------------------

main =
    render $ fold
      [ h1 (text "Free CRUD monad")
      , pt "Ho ho ho!"
      ]
  where pt = p <<< text

------------------------------------------------------------------

type PersonRec =
  { id   :: Maybe PersonId
  , name :: String
  , year :: Int
  }

type PersonId = Int

newtype Person = Person PersonRec

type CompanyRec =
  { id      :: Maybe CompanyId
  , ownerId :: PersonId        -- a Company must have an owner
  , name    :: String
  }

type CompanyId = Int

newtype Company = Company CompanyRec

------------------------------------------------------------------

-- TODO hack; wrapping up entities of different types (Person,
--      , Company, ...) in a sum type like this allows us to
--      store entities in Crud constructors such that they all
--      have the same type (Entity); otherwise we'd need something 
--      like `| forall e. Create e a` where e is an entity type.
--
--      This means that we'd have to write/generate domain
--      (schema, app) specific data types.
data Entity
  = PersonE  Person
  | CompanyE Company

data CrudF next
  = Create Entity next

type Crud = Free CrudF

-- create :: Entity -> Crud DbId
-- create x = liftF (Create x 42)

createPerson :: Person -> Crud DbId
createPerson x = liftF (Create (PersonE x) 42)

createCompany :: Company -> Crud DbId
createCompany x = liftF (Create (CompanyE x) 42)

------------------------------------------------------------------

-- TODO hack, unifies PersonId and CompanyId which are both aliases for Int atm
type DbId = Int