anchor.diff:          (if (member (first function-name)
                       '(com.informatimago.common-lisp.lisp.stepper:lambda lambda))
               `(progn
  -               ;; (print '(2) *step-trace-output*)
  -               (simple-step `(,(step-lambda function-name :environment env)
  +               ,(simple-step `(,(step-lambda function-name :environment env)
                                  ,@(mapcar (lambda (argument) (step-expression argument env))
                                            arguments))
  -                            form))
  +                             `,form))
               (error "Invalid object used as function name ~S in function call ~S"
                      function-name form))
           `(progn
  -           ;; (print '(3) *step-trace-output*)
              ,(simple-step `(,function-name
                              ,@(mapcar (lambda (argument) (step-expression argument env))
                                        arguments))
                            form)))))
   
  +(defvar *implementation-specific-special-operators* '()
  +  "An a-list mapping symbols to macro-functions expanding an implementation specific special-operator.")
  +
  +#+ccl (push (cons 'ccl:compiler-let (lambda (whole environment)
  +                                      (declare (ignore environment))
  +                                      (destructuring-bind (clet (&rest bindings) &body body) whole
  +                                        (declare (ignore clet bindings))
  +                                        `(progn ,@body))))
  +            *implementation-specific-special-operators*)
   
   (defun step-expression (form env)
     ;; Operators in CL-STEPPER are macros, so they're taken care of
  
positive.code:     ;; The other atoms are unchanged:
      ((atom form)     `(self-evaluating ,form))
      ;; Now we have a list.
      (t
       (case (first form)
  
         ;; First we check the real CL special operators:
         ;; We map them to cl-stepper operators and step the mapped version.
         ((function quote)
  
negative.code: ;;;;LEGAL
  ;;;;    AGPL3
  ;;;;
  ;;;;    Copyright Pascal J. Bourguignon 2012 - 2022
  ;;;;
  ;;;;    This program is free software: you can redistribute it and/or modify
  ;;;;    it under the terms of the GNU Affero General Public License as published by
  