Quasi-bug/strange behavior in error reporting [long]

Jim Witte jswitte at bloomington.in.us
Wed Apr 23 15:10:01 CDT 2003


Hi,

   This probably really should go to the improve-rev list, but I'm not a 
professional license holder, so..

   I've got a stack that uses a mousedown handler in the card script to 
perform a variety of different actions depending on a variable gMode 
(yeah, it would probably be cleaner [and a bit faster] if I used an 
insert script command.. that's for Apparent Motion v2).  Here's the 
relevant snippets of code: (In this example, gMode is "delete")

on mousedown
   global gMode
  if within(graphic "leftFrame", it) then
   switch gMode
   case "create"
     [..]
   case "delete"
     deleteObj
     break [..]
end mousedown

on deleteObj
   if not checkMouseControl() then
     exit deleteObj
   else
     [*] get the mouseControl
     put id of it into objId [..]
end deleteObj

   The checkMouseControl function just returns true if the mouse is over 
an appropriate control (a display object in this case).

   As written, the script works fine for deleting objects.  But if I 
comment out the starred line, it breaks - which I expect, because I 
don't have the mouseControl in it anymore [side note: the 
getMouseControl function does say 'get the mouseControl' but the it 
variable must not carry outside of the function's scope].

   But the odd thing is the error it gives me.  I would expect it to say 
there was some kind of error in the deleteObj handler, as that is where 
the undefined 'it' is referenced.  But instead, it says:

Type: switch: error in statement
Object: Image 1
Line: if within(graphic "leftFrame", it)
Hint: it

which seems to indicate that the error occurs not in the deleteObj 
handler, but in the mousedown handler.  Is the reason this apparent 
error-report inconsistency happens due to the way the engine "inlines" 
the handlers together when compiling the script down to a bytecode?

Thanks,
Jim




More information about the use-livecode mailing list