Help me understand this code please

[rdogomes]

Hi have this code in a routine I got from the internet, I know what it does but I don't understand it... Could someone explain?

(defun C:sumlp (/ p l e sxy exy sum)
   (setq p  (ssget   (list (cons -4 "<or")
                              (cons 0 "LINE")
                              (cons 0 "LWPOLYLINE")
                              (cons -4 "<and")
                                 (cons 0 "POLYLINE")
                                 (cons -4 "<not")
                                    (cons -4 "&") (cons 70 (+ 16 32 64))
                                 (cons -4 "not>")
                              (cons -4 "and>")
                           (cons -4 "or>")
                     )
            )
         sum 0.0
   )

Thanks a lot

[ccowgill]

Hi have this code in a routine I got from the internet, I know what it does but I don't understand it... Could someone explain?

(defun C:sumlp (/ p l e sxy exy sum)
   (setq p  (ssget   (list (cons -4 "<or")
                              (cons 0 "LINE")
                              (cons 0 "LWPOLYLINE")
                              (cons -4 "<and")
                                 (cons 0 "POLYLINE")
                                 (cons -4 "<not")
                                    (cons -4 "&") (cons 70 (+ 16 32 64))
                                 (cons -4 "not>")
                              (cons -4 "and>")
                           (cons -4 "or>")
                     )
            )
         sum 0.0
   )

Thanks a lot

Welcome to AUGI and congrats on your first post.
this code allows the user to select any object that is a line or polyline, as long as the polyline is not a 3d polygon mesh that is closed in the n direction and that is not a polyface mesh and sets the selection set to the variable p, as well as setting sum equal to 0.0. But I dont think it will do what it is intended as typically dxf codes are not considered bitwise, meaning, you cant use a sum, you would have to specify each 70 group individually.

[rkmcswain]

But I dont think it will do what it is intended as typically dxf codes are not considered bitwise, meaning, you cant use a sum, you would have to specify each 70 group individually.

It works in my tests, and the documentation agrees.
It says "The bitwise AND, "&", is true if ((integer_group & filter) /= 0)—that is, if any of the bits set in the mask are also set in the integer group."

Which in this case is the same as saying... (logand value (+ 16 32 64)), and as examples...

* (logand 16 (+ 16 32 64)) returns 16 [this is a 3D mesh polyline]
* (logand 128 (+ 16 32 64)) returns 0 [this is a plain closed polyline]

[ccowgill]

It works in my tests, and the documentation agrees.
It says "The bitwise AND, "&", is true if ((integer_group & filter) /= 0)—that is, if any of the bits set in the mask are also set in the integer group."

Which in this case is the same as saying... (logand value (+ 16 32 64)), and as examples...

* (logand 16 (+ 16 32 64)) returns 16 [this is a 3D mesh polyline]
* (logand 128 (+ 16 32 64)) returns 0 [this is a plain closed polyline]

I've learned something today, I'm going home now

[rdogomes]

Thanks a lot for the replies

I also learned today that I have a lot to learn.. I don't get most of what has been said.

But perhaps I didn't phrase my question well enough.

I know what the code does, but I don't know how

sorry if my english sounds strange

[ccowgill]

the list is a filter that applies to the selection set, when an object is selected, its properties are matched against the filter list and if the object meets those filter requirements, it is allowed to be added to the selection set, otherwise it is discarded. if you look up the SSGET function in the developer help, it will give you some additional information.

[rdogomes]

more specifically what I don´t understand is all those "<or" "<and" "&", and that part (cons 70 (+ 16 32 64)

I can't seem to find the info about those kinds of conditionals, does anyone know?

[rdogomes]

I think I found something in the help file about relational tests... I'm starting to understand it.

[RobertB]

more specifically what I don´t understand is ... that part (cons 70 (+ 16 32 64)

I can hit this one. That particular DXF code (70) stores a bit-value. So instead of simply providing the sum, e.g. '(70 . 112), the author is showing, in the code, which bits we are concerned about, e.g. (+ 16 32 64). If you want to understand why showing bit values in this fashion makes sense, see this post.