Structs

Elchemy represents all the structs as maps, so a struct defined like

human : { name : String
        , age : Int
        }

Is an equivalent of

@spec human :: %{name: String.t(), age: integer()}

Also type aliases denoting structs can be instantiated like functions

type alias Human =
     { name : String
     , age : Int
     }

Human "Krzysztof" 22

Struct polymorphism

What's more structs can describe a map that has at least specified elements using an update syntax.

type alias Employee x =
     { x
     | salary : Int
     }

Which means any struct that has a field salary of type integer. That way we can define our pseudo-inheritance and polymorphism for more advanced structures.

type alias Human =
     Employee
        { name : String
        , age : Int }

human : Human

Would resolve to

@spec human :: %{
  salary: integer(),
  name: String.t,
  age: integer()
}

But be advised that using this "polymorphic" approach strips us from the ability to use type aliases as constructors.