A Elixir Parser - Transforming a List of Tokens into a "Tree" (List of List)

gistfile1.ex

defmodule Parser do

    def read(input) do
        tokens = Tokenizer.tokenize(input)
        parse tokens, []
    end

    def parse([], stack) do
        stack
    end

    #the input comes in the form of: ["(", "foo", "1", "(", "bar", "2", ")", ")"]
    #and shall produce:              [:list, "foo", "1", [:list, "bar", "2"]]
    def parse(input, stack \\ []) do
        [token | tail] = input
        case token do
            "(" -> 
                stack = stack ++ [[:list]]
            ")" -> 
                last = List.last(stack)
                stack = List.delete_at(stack, -1)
                if stack != [] do
                    prev = List.last(stack)
                    stack = List.delete_at(stack, -1)
                    prev = prev ++ [last]
                    stack = stack ++ [prev]
                else
                    stack = last
                end
            _ -> 
                last = List.last(stack)
                stack = List.delete_at(stack, -1)
                last = last ++ [token]
                stack = stack ++ [last]
        end
        parse tail, stack
    end
end