Date   : Sun, 03 Jul 2005 23:38:03 +0100 (BST)
From   : Greg Cook <debounce@...>
Subject: This program will self destruct

A little something to clear the air...

>LIST
   10 DIM B% 4
   20 PROCg(1,2)
   30 END
   40 DEF PROCg(?B%,B%!1)
   50 PRINT "This program will self destruct"
   60 ENDPROC
>RUN
This program will self destruct
>RUN

Syntax error at line 20
>LIST 20
   20
     1,2)
>

So it's not safe to write instant-whip wrappers for the OSFILE, OSGBPB
calls etc, anything besides non-overlapping !X or X!N values has to be
assigned through "idler" variables:

   40 DEF FNg(A%,B%!1)
   50 LOCAL C%
   60 C%=?B%
   70 ?B%=A%
   80 PRINT "Phew! Mission accomplished"
   90 ?B%=C%
  100 ENDPROC

You may know that the actual parameters of PROCs and FNs are
automatically made LOCAL but restored in reverse order, which is why
the ! fields must not overlap.  But the ? operator really goes wrong. 
Even this fails to do its job:

   50 LOCAL ?B%

You have been warned!

Greg Cook
debounce@...
http://homepages.tesco.net/~rainstorm/



               
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