tdefinitions.lisp - clic - Clic is an command line interactive client for gopher written in Common LISP
HTML git clone git://bitreich.org/clic/ git://hg6vgqziawt5s4dj.onion/clic/
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tdefinitions.lisp (1656B)
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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))))