anchor.diff:  clauses -> clause clauses : ['$1'|'$2'].
   clauses -> clause : ['$1'].
   
  -clause -> when inline_exprs eol expr_list : 
  +clause -> when inline_exprs eol body : 
     #clause{
       line=?line('$1'), 
       patterns='$2', 
  
positive.code:   class_decl
    functions
    function
    function_body
    pargs
    pargs_tail
    block_capture
  
negative.code:     body  = '$5'
    }.
  
  body -> '$empty'  : [#nil{}].
  body -> expr_list : '$1'.
  
  %% Class instantiations
  class_inst -> module_name pargs :
  