Function definition and currying

Function definition

To define a function that gets exported you need to declare a type for it with

functionName : ArgType -> ArgType2 -> ReturnType

And a function body underneath

functionName argOne argTwo = body

This will output following definition:

curry function_name/2
@spec function_name(arg_type, arg_type2) :: return_type
def function_name(arg_one, arg_two) do
  body
end

Following rules apply:

1. A function will use def or defp based on exposing clause at the top of the module
2. The name of the function as well as its spec will always be snake_cased version of the camelCase name
3. curry function/arity is a construct that makes the function redefined in a form that takes 0 arguments, and returns X times curried function (2 times in this example). Which means that from elixir our function can be called both as: function_name(arg_one, arg_two) or function_name().(arg_one).(arg_two) and it won't have any different effect
4. @spec clause will always resolve types provided, to a most readable and still understandable by the elixir compiler form

Curried definition

Because of the curried nature of Elm function definitions we can just make our function return functions

For example instead of writing

addTwo : Int -> Int
addTwo a = 2 + a

We could just write

addTwo : Int -> Int
addTwo = (+) 2

In which case Elchemy will recognize a curried return and still provide you with a 1 and 0 arity functions, not only the 0 one. And output of such a definition would look like:

curry add_two/1
@spec add_two(integer) :: integer
def add_two(x1) do
   (&+/0).(2).(x1)
end

Which basically means that Elchemy derives function arity from the type, rathar then function body