Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uflorida!haven!mimsy!brillig.umd.edu!spector
From: spector@brillig.umd.edu (Lee Spector)
Newsgroups: comp.sys.mac.hypercard
Subject: Message Window: probs w/global variables
Message-ID: <19503@mimsy.UUCP>
Date: 10 Sep 89 03:50:30 GMT
Sender: nobody@mimsy.UUCP
Reply-To: spector@brillig.umd.edu.UUCP (Lee Spector)
Organization: University of Maryland, Dept. of Computer Sci.
Lines: 45

Since I don't like the fact that the message box contains only one line
(causing old commands and results to be lost) I've been trying to hack
together a "message window" that'll act like windows in other interpreted
languages.  (Sort of like a "listener" window in Lisp).  The basics are
easy: grab the last line of the window, evaluate it somehow (by calling "do",
moving it to the message box, or some other trick), put the result into the
next line of the window, and scroll appropriately.  By making this into a
"returnInField" handler for the field you can get reasonable results.

HOWEVER, things get considerably worse when you try to set global variables
from your window.  For example, try "put 5 into j".  Following this with
"j <return>" gets you a "Can't understand j" message BECAUSE j WAS NOT SET
GLOBALLY.  This is true whether you evaluate with "do" or by moving the
relevant line to the message box and sending EnterKey.  Now I don't know
what rules HyperCard uses for variable scoping (is this written up anywhere?
Is it even consistent?) but by playing around I've found that I CAN set the
variable globally by creating, on the fly, a script for a hidden field that
looks like this:

 on kludge
  global j
  put 5 into j
 end kludge

Then I can send a "kludge" message to the hidden field to set the variable
globally.  HOWEVER, I must also do this sort of thing to REFER to j; that
is, in order to beable to type "j" and get 5 I must stuff it into a script
with the appropriate "global" statement.  NOW THIS GETS REALLY MESSY, because
the script has to have a different form depending on whether the given line 
is a command (like put...) or an expression (like 2 + 2).  Further, if I want
to allow for arbitrary references to global variables then I'll have to do
something very complicated (?).  In short, I'd have to rewrite the hypertalk
language parser and implement a copy of its run-time symbol table as well!

I conclude that there must be (BETTER BE) a better way.  How can I evaluate
a string JUST AS THOUGH I HAD TYPED IT TO THE MESSAGE BOX AND TYPED RETURN?
It seems like you could just script this, but as far as I can tell the fact
that it's scripted changes the scope of the variables in the string.

If anyone has any insights, knows of a write-up of HyperTalk's scoping rules,
or knows of an already-written message window package, please let me know.

Thanks! 

  -Lee (spector@brillig.umd.edu)