anchor.diff:  functions -> eol functions : '$2'.
   functions -> function eol functions : ['$1'|'$3'].
   
  +%% Function identifiers
  +function_identifier -> identifier : '$1'.
  +function_identifier -> punctuated_identifier : '$1'.
  +
   %% Function definitions
   function -> def function_identifier eol expr_list 'end' : 
     #function{
  
positive.code:     body='$7'
    }.
  
  %% Function identifiers
  function_identifier -> identifier : '$1'.
  function_identifier -> punctuated_identifier : '$1'.
    
  %% Boolean values
  boolean -> true  : '$1'.
  
negative.code: 
  %% Bound variables
  bound_var -> '^' identifier : #bound_var{line=?line('$1'), name=element(3, '$2')}.
  
  %% Index operation
  call -> call_expr '[' expr ']' :
  