anchor.diff:  function_identifier -> punctuated_identifier : function_identifier('$1').
   function_identifier -> class : function_identifier('$1').
   
  +%% Function references
  +funref -> funcall_expr '.' function_identifier : {funref, line('$2'), '$1', '$3'}.
  +
   %% Function calls
   funcall -> function_identifier '(' ')' : {funcall, line('$2'), '$1', [], {atom, line('$2'), nil}}.
   funcall -> function_identifier '(' exprs ')' : {funcall, line('$2'), '$1', '$3', {atom, line('$2'), nil}}.
  
positive.code:   class_decl
    functions
    function
    funcall_expr
    funcall
    function_identifier
  
negative.code: 
  unary_expr -> unary_op unary_expr : {op, line('$1'), op('$1'), '$2'}.
  unary_expr -> '!' unary_expr : {op, line('$1'), 'not', '$2'}.
  unary_expr -> funref_expr : '$1'.
  
  funref_expr -> funref : '$1'.
  funref_expr -> funcall_expr : '$1'.
  
  funcall_expr -> funcall : '$1'.
  funcall_expr -> class_inst_expr : '$1'.
  