anchor.diff:    "An alist mapping lexical-variables to their values, if known.")
   
   (defparameter *constprop-lambda-copy-limit* 3)
  +(defparameter *constant-fold-modes* (make-hash-table :test 'equal))
   
   (defun constprop (lambda architecture)
     (declare (ignore architecture))
  
positive.code:              (keywordp (symbol))
               (sys.int::%type-check (t fixnum t))
               (float (t t))))
    (setf (get (first x) 'constant-fold-mode) (second x))
    (when (third x)
      (setf (get (first x) 'constant-folder) (third x))))
  
  (defun mark-as-constant-foldable (name)
    (setf (get name 'constant-fold-mode) t))
  
negative.code: (defun constant-fold (form function arg-list)
    ;; Bail out in case of errors.
    (ignore-errors
      (let* ((info (gethash function *constant-fold-modes*))
             (mode (car info))
             (folder (or (cdr info) function)))
        (etypecase mode
          (cons
           ;; List of arguments & argument types.
  