Lisp工具包(ltk)：无法获取SCALE :变量值

Question

我在一台AMD64机器上使用SBCL for Linux。函数控制-测试生成一个带有画布和两个滑动刻度的窗口。滑块:上面滑块和前面滑块的变量应该分别绑定到上面的THETA和前面的THETA，但更新代码只看到0。我已经在另一个函数中测试了更新代码。

(defun controltest ()
  "Test of a user-controlled robot arm"
  (with-ltk ()
    ; (make-instance 'scale :master fscale :from 0 :to 100  :length 150 )
    (let* ((upper-theta 0) (fore-theta 0)
       (upper-slider 
        (make-instance 'scale :from 0 :to 7 
               :length  360 :variable upper-theta))
       (fore-slider 
        (make-instance 'scale :from 0 :to 7
               :length  360 :variable fore-theta))
       (cnvs (make-instance 'canvas :width cnvs-width :height cnvs-height))
       (upper (manip:uctk-beam :cen-x 200 :cen-y 200 
                   :b-length 40 :b-width 20
                   :tk-cnvs cnvs))
       (fore (manip:uctk-beam :cen-x 0 :cen-y 40 ; relative to upper
                  :b-length 40 :b-width 20
                  :tk-cnvs cnvs))
       (slp-time 50))
      (labels ((update ()
         (draw upper nil) ; contains FORE, no need to draw separately
         (geo:set-member-theta upper 2 fore-theta)
         (geo:set-theta upper upper-theta)
         (after slp-time #'update)))
    (geo:add-geo upper fore) ; make FORE a member of UPPER
    (pack cnvs :fill :both :expand 1)
    (pack upper-slider :side :bottom)
    (pack fore-slider :side :bottom)
    (update))))) 

Answer 1

请原谅，我似乎没有进行尽职调查，这个问题在3年前在以下位置得到了回答：http://permalink.gmane.org/gmane.lisp.ltk.user/329

答案是传递给:VARIABLE的名称实际上不会自动更新。我将LAMBDA表达式传递给:COMMAND关键字，而不是乱搞:VARIABLE；因此，下面的方法是正确的：

(upper-slider 
        (make-instance 'scale :from 0 :to 7 
               :length  360 
               :command (lambda (val) (setq upper-theta val))))
(fore-slider 
        (make-instance 'scale :from 0 :to 7 
               :length  360 
               :command (lambda (val) (setq fore-theta val))))