anchor.diff:  (defun let-bindings (stmt)
     (match stmt
       (('let bindings . _) bindings)
  -    (_ (error (format nil "invalid statement: ~A" stmt)))))
  +    (_ (error "invalid statement: ~A" stmt))))
   
   (defun let-statements (stmt0)
     (match stmt0
       (('let _ . stmts) stmts)
  -    (_ (error (format nil "invalid statement: ~A" stmt0)))))
  +    (_ (error "invalid statement: ~A" stmt0))))
   
   (defun compile-let (stmt0 type-env def)
     (let ((bindings (let-bindings stmt0))
  
positive.code:      (compile-variable-reference exp type-env def))
      ((inline-if-p exp) (compile-inline-if exp type-env def))
      ((function-p exp) (compile-function exp type-env def))
      (t (error (format nil "invalid expression: ~A" exp)))))
  
  (defun literal-p (exp)
    (or (int-literal-p exp)
  
negative.code:                         (compile-identifier var)
                          (compile-expression exp type-env def))
                  (%compile-let rest stmts type-env2 def))))
      (_ (error "invalid bindings: ~A" bindings))))
  
  (defun compile-let-statements (stmts type-env def)
    (compile-progn-statements stmts type-env def))
  