anchor.diff:  (defmethod shcl/core/lexer:token-value ((sigil sigil-token))
     nil)
   
  -(defun completion-suggestions-for-start-of-new-token (leading-tokens)
  +(defun valid-types-for-next-token (leading-tokens)
     (let* ((sigil-token (make-instance 'sigil-token))
            (command-iterator (shcl/core/shell-grammar:command-iterator
                               (lookahead-iterator-wrapper
  
positive.code:       (vector-push-extend error all-errors))
      (setf error (make-instance 'shcl/core/parser:choice :errors all-errors))
      (iterator-without-duplicates
       (concatenate-iterators
        (map-iterator (expected-types-for-parse-error error sigil-token)
                      'simple-expansions-for-type)))))
  
  (defun completion-suggestions-for-input (input-text cursor-point readtable)
    "Compute possible completions.
  
negative.code: (defvar *empty-iterator*
    (make-iterator ()
      (stop)))
  
  (defun iterator-without-duplicates (iter)
    (let ((seen-values (fset:empty-set)))
  