anchor.diff:  %%% as unadorned binaries, and accept that mutation is unavailable.
   %%% R5RS did not have bytevectors, they were added in R6RS and R7RS.
   %%%
  -%%% port		<an arity-0 closure from module es_port_wrapper>
  +%%% port                <an arity-0 closure from module es_port_wrapper>
   %%%
   %%% [NYI]
   %%% Scheme requires ports to be a distinct type.  We relax that
  
positive.code: %%%
  %%% Maps between Scheme datums and their Erlang representations.
  %%%
  %%% Scheme		Erlang
  %%% ======		======
  %%%
  %%% Straight-forward mappings:
  %%%
  %%% null		[]
  %%% number		integer or float
  %%% symbol		atom (with some exceptions)
  %%%
  %%% Slightly non-obvious mappings:
  %%%
  %%% pair		[_ | _]
  %%%
  %%% Scheme pairs are similar to Erlang list cells, except
  %%% for the fact that list cells are immutable.  We map pairs
  %%% to list cells, and accept that mutation is unavailable.
  %%%
  %%% #t			true
  %%% #f			false
  %%%
  %%% Scheme requires booleans to be disjoint from symbols,
  %%% but Erlang considers booleans to be special-case atoms.
  %%% We follow the Erlang convention.
  %%%
  %%% vector		tuple()
  %%%
  %%% Scheme vectors are similar to Erlang tuples, except
  %%% for the fact that tuples are immutable.  We map vectors
  %%% to tuples, and accept that mutation is unavailable.
  %%%
  %%% character		char()
  %%%
  %%% Scheme requires characters to be a distinct type, but
  %%% Erlang considers them to be a sub-range of the integers.
  %%% We represent them as unadorned integers.
  %%%
  %%% eof-object		fun es_datum:the_eof_object/0
  %%%
  %%% Scheme requires the eof-object to be a distinct type.
  %%% We relax that requirement and represent it as procedure
  %%% referencing es_datum:the_eof_object/0.
  %%% R5RS did not require this to be a distinct type.
  %%%
  %%% string		binary()
  %%% bytevector		<NYI -- should be binary()>
  %%%
  %%% Scheme requires strings and bytevectors to be distinct types,
  %%% but Erlang considers strings to be lists of characters while
  
negative.code: %%% that returns the corresponding handle (Pid).  The function closures
  %%% need to come from a reserved module to enable checking their type.
  %%%
  %%% procedure           Fun/N
  %%%
  %%% An Scheme procedure becomes an Erlang function of the same arity.
  %%% Variable-arity procedures are not supported.
  %%%
  %%% tid                 pid
  %%%
  %%% RnRS Scheme does not have threads, but ErlScheme adds threads
  %%% and maps them to Erlang processes.
  