anchor.diff:        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} ->
  
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: %%%   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
  