anchor.diff:  eval(Sexpr) -> eval(Sexpr, lfe_env:new()).  %Empty environment.
   eval(Sexpr, Env) -> lfe_eval:expr(Sexpr, Env).
   
  +'macro-function'(Symb) -> 'macro-function'(Symb, lfe_env:new()).
  +'macro-function'(Symb, Env) ->
  +    case lfe_env:get_mbinding(Symb, Env) of
  +        {yes,Macro} ->
  +            Macro;
  +        no -> []
  +    end.
  +
   macroexpand(Form) -> macroexpand(Form, lfe_env:new()).
   macroexpand(Form, Env) ->
       case lfe_macro:expand_expr(Form, Env) of
  -    {yes,Exp} -> Exp;
  -    no -> Form
  +        {yes,Exp} -> Exp;
  +        no -> Form
       end.
   
   'macroexpand-1'(Form) -> 'macroexpand-1'(Form, lfe_env:new()).
   'macroexpand-1'(Form, Env) ->
       case lfe_macro:expand_expr_1(Form, Env) of
  -    {yes,Exp} -> Exp;
  -    no -> Form
  +        {yes,Exp} -> Exp;
  +        no -> Form
       end.
   
   'macroexpand-all'(Form) -> 'macroexpand-all'(Form, lfe_env:new()).
  
positive.code: %% subst-if-not(New, Test, Tree) -> Tree.
  %% sublis(Alist, Tree) -> Tree.
  %% eval(Sexpr) -> Value.
  %% macroexpand(Form [,Environment]) -> {yes,Expansion} | no.
  %% macroexpand-1(Form [,Environment]) -> {yes,Expansion} | no.
  %% macroexpand-all(Form [,Environment]) -> {yes,Expansion} | no.
  
  is_lfe_bif(acons, 3) -> true;
  is_lfe_bif(pairlis, 2) -> true;
  
negative.code: 
  %% Standard lisp library.
  -export([is_lfe_bif/2,
           acons/3,pairlis/2,pairlis/3,
           assoc/2,'assoc-if'/2,'assoc-if-not'/2,
           rassoc/2,'rassoc-if'/2,'rassoc-if-not'/2,
           subst/3,'subst-if'/3,'subst-if-not'/3,sublis/2,
           eval/1,eval/2,
           'macro-function'/1,'macro-function'/2,
           macroexpand/1,macroexpand/2,
           'macroexpand-1'/1,'macroexpand-1'/2,
           'macroexpand-all'/1,'macroexpand-all'/2]).
  
  %% Miscellaneous useful LFE functions.
  -export([format_exception/6,format_stacktrace/3]).
  