anchor.diff:  %% API functions
   %%====================================================================
   
  -sha256_init() -> "Undefined".
  +hash_init(sha256) ->
  +    sha256_init().
  +
   hash_update(_Context, _Data) -> "Undefined".
   hash_final(_Context) -> "Undefined".
   
  
positive.code: 
  %% API exports
  -export([
           sha256_init/0,
           hash_update/2,
           hash_final/1
          ]).
  
negative.code:     _ ->
        {error, "Could not find library"}
    end.
  
  sha256_init() -> "Undefined".
  