anchor.diff:  -behaviour(gen_server).
   
   %% API functions
  --export([start_link/0]).
  +-export([start_link/0,
  +         stop/0,
  +         evaluate/1]).
   
   %% gen_server callbacks
   -export([init/1,
  
positive.code: init([]) ->
      {ok, #state{context = erl_eval:new_bindings()}}.
  
  handle_call({eval, String}, _From, State) ->
      {ok, Ts, _} = erl_scan:string(String),
      {ok, Expr} = erl_parse:parse_exprs(Ts),
  
negative.code:          handle_info/2,
           terminate/2,
           code_change/3]).
  
  -record(state, {context}).
  
  