A startup function for interactive rc's is unnecessary

A startup function for interactive rc's is unnecessary

[Chris Siebenmann]

 After some thought, instead of hacking, I realized that all the
functionality of a function that's run on interactive startup can be
done with a prompt function. The trick is to figure out how to
recognize when you're in a new shell, and the easy way to do that is to
compare $pid against a saved version of it, so:
	fn prompt { if (~ $cpid $pid) {cpid=$pid; <initialize>} }
As an extra bonus, this gets run naturally even for login shells.

 This leaves the question of whether there's any use for a function
executed automatically at the start of non-interactive rc shells;
I can't think of any.

	- cks

Re: A startup function for interactive rc's is unnecessary

[John Mackin]

Chris points out the following:

     After some thought, instead of hacking, I realized that all the
    functionality of a function that's run on interactive startup can be
    done with a prompt function. The trick is to figure out how to
    recognize when you're in a new shell, and the easy way to do that is to
    compare $pid against a saved version of it, so:
    	fn prompt { if (~ $cpid $pid) {cpid=$pid; <initialize>} }
    As an extra bonus, this gets run naturally even for login shells.

There is actually an improvement on this idea, which I thought of
some weeks ago but didn't suggest on the list since I wasn't sure it
was really OK.  I finally got around to asking Byron about it, and he
showed me why it is legal (my cursory inspection of the code didn't
encompass the relevant part), so: just define the prompt function to
do whatever initialisation you want to happen before the first prompt
_and then delete itself_ (or, if you still want a prompt function,
redefine itself):

	fn prompt {
		... initialise ...
		fn prompt		# or, "fn prompt { normal-prompt-func }"
	}

OK,
John.