小编mas*_*agi的帖子

下面的程序似乎非常低效.它需要多达28.980 GC时间,相比之下6.361秒非GC时间,SBCL为1.0.53.

(deftype vec3 () '(simple-array double-float (3)))

(declaim (inline make-vec3 vec3-zero
             vec3-x vec3-y vec3-z
             vec3-+))

(defun make-vec3 (x y z)
  (declare (optimize (speed 3) (safety 0)))
  (make-array 3 :element-type 'double-float
                :initial-contents (list x y z)))

(defun vec3-zero ()
  (make-vec3 0.0d0 0.0d0 0.0d0))

(defun vec3-x (x)
  (declare (optimize (speed 3) (safety 0)))
  (declare (type (simple-array double-float (3)) x))
  (aref x 0))

(defun vec3-y (x)
  (declare (optimize (speed 3) (safety 0)))
  (declare (type (simple-array double-float (3)) x))
  (aref x 1))

(defun …

我想映射申请表格.

类似地图的函数类型如下:

mapX :: (Applicative f) => (f a -> f b) -> f [a] -> f [b]

用作:

result :: (Applicative f) => f [b]
result = mapX f xs
  where f  :: f a -> f b
        f = ...
        xs :: f[a]
        xs = ...

作为这篇文章的背景,我尝试用Paul Haduk的"The Haskell School of Expression"使用Applicative样式编写流体模拟程序,我想用Applicative样式表达模拟如下:

x, v, a :: Sim VArray
x = x0 +: integral (v * dt)
v = v0 +: integral (a * dt)
a = (...calculate acceleration …

初始化数据结构或对象时,如果子对象在使用后需要显式释放过程,那么在初始化过程中如何处理错误？

让我举个例子,用SUBOBJ1和SUBOBJ2槽初始化一个OBJECT对象,设置指向int值的外部指针:

(defun init-object ()
  (let ((obj (make-object)))
    (setf (subobj1 obj) (cffi:foreign-alloc :int)
          (subobj2 obj) (cffi:foreign-alloc :int))
    obj))

如果我们在SUBEJ2插槽的FOREIGN-ALLOCing中出错,我们应该为SUBOBJ1插槽执行FOREIGN-FREEing以避免内存泄漏.

作为一个想法,我可以写如下:

(defun init-object ()
  (let ((obj (make-object)))
    (handler-case
        (setf (subobj1 obj) (cffi:foreign-alloc :int)
              (subobj2 obj) (cffi:foreign-alloc :int))
      (condition (c)   ; forcedly handling all conditions
        (when (subobj1 obj) (cffi:foreign-free (subobj1 obj)))
        (error c)))    ; invoke the condition c again explicitly
    obj))

你有更好的想法,或一般惯用的模式？

谢谢

在答案之后,我使用UNWIND-PROTECT添加代码.它不起作用,因为即使所有分配都成功完成,解除分配形式也会运行.

(defun init-object ()
  (let ((obj (make-object)))
    (unwind-protect
      (progn
        (setf (subobj1 obj) (cffi:foreign-alloc :int)
              (subobj2 obj) (cffi:foreign-alloc :int))
        obj) …

什么是事实上的便携式外部程序调用的Common Lisp库？

我在这里找到了两个这样的库.

• 遗嘱执行人;
• 外部程序.

还有其他什么吗？