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From: vishniac@wanginst.UUCP (Ephraim Vishniac)
Newsgroups: net.micro.mac
Subject: Re: Mac "Make"
Message-ID: <1032@wanginst.UUCP>
Date: Thu, 5-Sep-85 09:52:14 EDT
Article-I.D.: wanginst.1032
Posted: Thu Sep  5 09:52:14 1985
Date-Received: Sat, 7-Sep-85 05:24:38 EDT
References: <8509040349.AA09171@ucbkim.ARPA>
Organization: Wang Institute, Tyngsboro, Ma.  01879
Lines: 26

> A number of programs provide the ability to invoke another program.  Others
> such as the "transfer" desk accessory, the finder, and the minifinder, regain
> control once another program terminates.
> 
> Can someone explain how to this mechanism works?  It occurs to me that it
> might not be too hard to get a public domain "make" program to run on the
> Mac.
> 
I know of two ways that one can gain control between application programs.
If you mean to completely replace the finder, you install your program by
setting it as the "shell" application.  This is one of the items stored
at the front of the boot sectors on your disk.  After IPL, the name of the
shell is stored in low memory, so you can change shells on the fly.

The sneakier method is to use _GetTrapAddress and _SetTrapAddress to insert
some of your own code into the _Launch and _ExitToShell traps.  For example,
you could patch yourself into the _ExitToShell trap to give the user the
choice of launching another program or continuing into the real finder.
Although I haven't checked to be sure, I imagine that this is the way
the SkipFinder DA operates.

-- 
Ephraim Vishniac
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  vishniac%Wang-Inst@Csnet-Relay