🚀 go-pugleaf

>From Craig.Everhart@CMU-10A Mon Mar  1 11:07:33 1982
I see no reason why an editor should by default allow an edit session to
proceed with the file-being-edited unlocked, certainly not after the user
makes the first change to his image of the file.  How this is integrated into
the user interface is largely a matter of taste; however, it's highly annoying
to have made lots of changes to a file only to find that they really weren't
being made to the file at all, because you couldn't write them back out
without clobbering something unknown.  Better to find out that someone else
is editing the same file either as you start looking at it or as you make your
first change.

The situation is reminiscent of a circa-1975 feature of CMU's mail sender; it
would let you type in an arbitrarily-long message, then once you had finished
it would notice that you had mis-typed your recipient's name, so it wouldn't
send the mail.  I think it didn't save a copy of what you had typed, either.