elixir/lib/mix/tasks/step3_env.ex

   1 defmodule Mix.Tasks.Step3Env do
   2   @initial_env %{
   3     "+" => &+/2,
   4     "-" => &-/2,
   5     "*" => &*/2,
   6     "/" => &div/2
   7   }
   8
   9   def run(_) do
  10     {:ok, env} = Mal.Env.initialize()
  11     Mal.Env.merge(env, @initial_env)
  12     main(env)
  13   end
  14
  15   def main(env) do
  16     IO.write(:stdio, "user> ")
  17     IO.read(:stdio, :line)
  18       |> read_eval_print(env)
  19
  20     main(env)
  21   end
  22
  23   def eval_ast(ast, env) when is_list(ast) do
  24     Enum.map(ast, fn elem -> eval(elem, env) end)
  25   end
  26
  27   def eval_ast({:symbol, symbol}, env) do
  28     case Mal.Env.get(env, symbol) do
  29       {:ok, value} -> value
  30       :not_found -> throw({:error, "invalid symbol #{symbol}"})
  31     end
  32   end
  33
  34   def eval_ast(ast, _env), do: ast
  35
  36   def read(input) do
  37     Mal.Reader.read_str(input)
  38   end
  39
  40   defp eval_bindings([], _env), do: _env
  41   defp eval_bindings([{:symbol, key}, binding | tail], env) do
  42     evaluated = eval(binding, env)
  43     Mal.Env.set(env, key, evaluated)
  44     eval_bindings(tail, env)
  45   end
  46   defp eval_bindings(_bindings, _env), do: throw({:error, "Unbalanced let* bindings"})
  47
  48
  49   def eval([{:symbol, "def!"}, {:symbol, key}, value], env) do
  50     evaluated = eval(value, env)
  51     Mal.Env.set(env, key, evaluated)
  52     evaluated
  53   end
  54
  55   def eval([{:symbol, "let*"}, bindings, body], env) do
  56     {:ok, let_env} = Mal.Env.initialize(env)
  57     eval_bindings(bindings, let_env)
  58     eval(body, let_env)
  59   end
  60
  61   def eval(ast, env) when is_list(ast) do
  62     [func | args] = eval_ast(ast, env)
  63     apply(func, args)
  64   end
  65
  66   def eval(ast, env), do: eval_ast(ast, env)
  67
  68   def print(value) do
  69     IO.puts(Mal.Printer.print_str(value))
  70   end
  71
  72   def read_eval_print(:eof, _env), do: exit(0)
  73   def read_eval_print(line, env) do
  74     read(line)
  75       |> eval(env)
  76       |> print
  77   catch
  78     {:error, message} -> IO.puts("Error: #{message}")
  79   end
  80 end