Option.ex

defmodule Option do 

    def some(value) do 
        {:some, value }
    end 

    def none() do 
        nil
    end

    def pure(value) do 
        some(value)
    end 

    def map(option, function) do 
        case option do 
            {:some, value} -> {:some, function.(value) }
            nil -> nil 
            _ -> throw("Illegal value: #{option} is not an option.")
        end 
    end

    def bind(option, function) do 
        case option do 
            {:some, value} -> function.(value)
            nil -> nil
            _ -> throw("Illegal value: #{option} is not an option.")
        end 
    end 

    def apply(value_option, function_option) do
        case { value_option, function_option } do 
            { {:some, value}, {:some, function} } -> pure(function.(value))
            { nil, _ } -> nil
            { _, nil } -> nil
            _ -> throw("Illegal values: one or more of #{value_option} and #{function_option} is not an option.")
        end 
    end

end