jjant

employeeFromDbToApplication : EmployeeFromDb1 -> List Employee1 -> Employee1
employeeFromDbToApplication (EmployeeFromDb1 empDb) employees =
    Employee1
        { id = empDb.id
        , name = empDb.name
        , age = empDb.age
        , employees = employees
        }

jjant

type alias Table1 =
    List EmployeeFromDb1



lookUpEmployee1 : Id -> Table -> Maybe Employee1
lookUpEmployee1 id table =
    table
        |> List.filter (\employee -> employee.id == id)
        |> List.head

jjant

type EmployeeFromDb1
    = EmployeeFromDb1
        { id : Id
        , name : String
        , age : Int
        , employerId : Id
        }

jjant

type alias Id =
    Int


type Employee1
    = Employee1
        { id : Id
        , name : String
        , age : Int
        , employees : List Employee1

jjant

map : (a -> b) -> Employee a -> Employee b
map f (Employee sharedData a) =
    Employee sharedData (f a)


replace : b -> Employee a -> Employee b
replace b =
    map (\_ -> b)

jjant

employeeAppToEmployeeCount : EmployeeApp -> EmployeeWithCount
employeeAppToEmployeeCount employeeApp =
    map (\employees -> List.length employees) employeeApp

jjant

zero :: FreeMonoid t
zero = Zero

(<>) :: FreeMonoid t -> FreeMonoid t -> FreeMonoid t
Zero <> x = x -- Left identity
x    <> Zero = x -- Right identity
(Combine t1 rest1) <> x =
  -- `(a <> b) <> x` is represented as `a <> (b <> x)`
  Combine t1 (rest1 <> x)

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interpret :: b -> (a -> b -> b) -> FreeMonoid a -> b
interpret myZero myCombine Zero = myZero
interpret myZero myCombine (Combine a rest) =
  a `myCombine` (interpret myZero myCombine rest) -- a `Combine` (b `Combine` Zero) -> a `myCombine` (b `myCombine` myZero)

jjant

isAdmin :: FreeMonoid (String, Bool) -> Bool
isAdmin perms = interpret True (\(_, perm) rest -> perm && rest) perms

isPowerUser :: FreeMonoid (String, Bool) -> Bool
isPowerUser perms = interpret False (\(_, perm) rest -> perm || rest) perms

isRegularUser :: FreeMonoid (String, Bool) -> Bool
isRegularUser perms = not (isPowerUser perms)

jjant

data FreeMonoid1 t
  = Zero
  | Val t
  | Combine (FreeMonoid1 t) (FreeMonoid1 t)