anchor.diff:  %%%   bodies as ASTs, not as S-expressions.
   %%% - Variadic functions (with "rest" parameters) are not supported, since
   %%%   they mess up calling conventions and interoperability with Erlang.
  +%%% - (set! ...) is restricted to assigning global variables in the REPL.
   %%%
   %%% Extensions:
   %%% - (: M F A) is equivalent to Erlang's fun M:F/A
  
positive.code: interpret_quote(Value) ->
    Value.
  
  interpret_try(Expr, Var, Body, EVar, Handler, _After = [], Env) ->
    interpret_try(Expr, Var, Body, EVar, Handler, Env);
  interpret_try(Expr, Var, Body, EVar, Handler, After, Env) ->
  
negative.code:       interpret_primop(PrimOp, Actuals, Env);
      {'ES:QUOTE', Value} ->
        interpret_quote(Value);
      {'ES:SET!', Var, Expr} ->
        'interpret_set!'(Var, Expr, Env);
      {'ES:TRY', Expr, Var, Body, EVar, Handler, After} ->
        interpret_try(Expr, Var, Body, EVar, Handler, After, Env);
      {'ES:TUPLE', Exprs} ->
  