Re: suprise with -=

[Ray Andrews <rayandrews@xxxxxxxxxxx>]

On 10/19/2015 05:27 PM, Bart Schaefer wrote:
> The parser doesn't know that "first" is an integer, or even that it's
> a variable that was previously declared.
That puzzles me.  Have not all your examples demonstrated that the 
parser is aware of the type of the variable and that it will perform 
it's operations accordingly?

   test2 ()
   {

       integer first=1 second=2

       third=first+second
       print A $third
       integer third
       print B $third

       integer fourth=first+second
       print C $fourth

   }
   A first+second    # 'third' is scalar so does the 'wrong' thing.
   B 0               # 'third' is now known to be integer by the 'print'.
   C 3               # 'fourth' is integer up front and remembered to
   be so.


I see very clearly that the type can change silently or sometimes not 
change at all and just sorta 'do nothing':

   test1 ()

   {

       integer first=1
       string1=foo

       first+=string1
       echo ${(t)first}
       echo "$first"

   }
   integer-local
   1            # The addition does nothing at all, but no error is thrown.


... and "${(t) ...}" is surely the demonstration that types are 
remembered?  I'm makinga deep error here, probably.


> The first shells didn't have integers or arrays at all.  They had only
> strings, and a few (external) programs like "expr" that could interpret
> strings of digits as numbers.
Thanks.  These 'history lessons' are invaluable (to me, anyway).  If 
anything besides strings were never anticipated in the original design 
of shells,then integers would bea 'tack on' and one could see that the 
whole issue of declarations/typing would behandled poorly.  The lesson 
is that one must be bloody careful. OTOH, whereas in Cif one wants to 
force a typecast it's a
labor, whereas in zsh one can do it not onlyeffortlessly, but even 
invisibly.
Powerful but dangerous.Caveat emptor.