definitions.lisp - clic - Clic is an command line interactive client for gopher written in Common LISP
 (HTM) git clone git://bitreich.org/clic/ git://enlrupgkhuxnvlhsf6lc3fziv5h2hhfrinws65d7roiv6bfj7d652fid.onion/clic/
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       ---
       definitions.lisp (1656B)
       ---
            1 (in-package :alexandria)
            2 
            3 (defun %reevaluate-constant (name value test)
            4   (if (not (boundp name))
            5       value
            6       (let ((old (symbol-value name))
            7             (new value))
            8         (if (not (constantp name))
            9             (prog1 new
           10               (cerror "Try to redefine the variable as a constant."
           11                       "~@<~S is an already bound non-constant variable ~
           12                        whose value is ~S.~:@>" name old))
           13             (if (funcall test old new)
           14                 old
           15                 (restart-case
           16                     (error "~@<~S is an already defined constant whose value ~
           17                               ~S is not equal to the provided initial value ~S ~
           18                               under ~S.~:@>" name old new test)
           19                   (ignore ()
           20                     :report "Retain the current value."
           21                     old)
           22                   (continue ()
           23                     :report "Try to redefine the constant."
           24                     new)))))))
           25 
           26 (defmacro define-constant (name initial-value &key (test ''eql) documentation)
           27   "Ensures that the global variable named by NAME is a constant with a value
           28 that is equal under TEST to the result of evaluating INITIAL-VALUE. TEST is a
           29 /function designator/ that defaults to EQL. If DOCUMENTATION is given, it
           30 becomes the documentation string of the constant.
           31 
           32 Signals an error if NAME is already a bound non-constant variable.
           33 
           34 Signals an error if NAME is already a constant variable whose value is not
           35 equal under TEST to result of evaluating INITIAL-VALUE."
           36   `(defconstant ,name (%reevaluate-constant ',name ,initial-value ,test)
           37      ,@(when documentation `(,documentation))))