with-struct.lisp

(defun psymb (package &rest args)
  (values (intern (apply #'mkstr args) package)))



(defmacro with-struct ((name . fields) struct &body body)
  (let ((gs (gensym)))
    `(let ((,gs ,struct))
       (let ,(mapcar #'(lambda (f)
                         `(,f (,(psymb (symbol-package name) name f) ,gs)))
                     fields)
         ,@body))))


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Example:

CL-USER 20 > (pprint (macroexpand-1 '(with-struct (foo- a b c) s (list a b c))))

(LET ((#:G7640 S))
  (LET ((A (FOO-A #:G7640))
        (B (FOO-B #:G7640))
        (C (FOO-C #:G7640)))
    (LIST A B C)))


You can now tell it which package to use:

CL-USER 21 > (pprint (macroexpand-1 '(with-struct (color::foo- a b c) s (list a b c))))

(LET ((#:G7641 S))
  (LET ((A (COLOR::FOO-A #:G7641))
        (B (COLOR::FOO-B #:G7641))
        (C (COLOR::FOO-C #:G7641)))
    (LIST A B C)))


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