Result.ex

defmodule Result do 

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

    def error(err) do 
        {:error, err}
    end

    def pure(value) do 
        ok(value)
    end 

    def map(result, function) do 
        case result do 
            {:ok, value} -> {:ok, function.(value)}
            {:error, e} -> {:error, e}
            _ -> throw("Illegal value: #{result} is not a result.")
        end 
    end

    def map_error(result, function) do 
        case result do 
            {:ok, value} -> {:ok, value}
            {:error, err} -> {:error, function.(err)}
            _ -> throw("Illegal value: #{result} is not a result.")
        end 
    end

    def bind(result, function) do 
        case result do 
            {:ok, value} -> function.(value)
            {:error, e} -> {:error, e}
            _ -> throw("Illegal value: #{result} is not a result.")
        end 
    end 

    def apply(value_result, function_result) do
        case {value_result, function_result} do 
            {{:ok, value}, {:ok, function}} -> pure(function.(value))
            {{:error, e}, _} -> {:error, e}
            {_, {:error, e}} -> {:error, e}
            _ -> throw("Illegal values: one or more of #{value_result} and #{function_result} is not a result.")
        end 
    end
end