Yes.  If it was =op, this means the C program probably used =+
instead of +=.  That was the
dialect of C that was around when Al was at Bell Labs.  The
transition from =+ to += was a
pain, but decreased errors dramatically (a=-1 vs a= -1).

We actually had a pretty good system for making changes like that. 
First, we would change
the compiler to accept both the old and the new.   Then we would
produce a warning
that on a particular date the old would no longer work.  Then we made
the old an error
and printed a message about how to fix it.   Eventually, we just let
it be a syntax error.
This process was applied many times on the way from typeless B to
strongly typed C.

----- Original Message -----
From: "Lars Brinkhoff" <lars@nocrew.org>
To:"Steve Johnson" <scj@yaccman.com>
Cc:<tuhs@tuhs.org>
Sent:Mon, 29 Oct 2018 07:31:24 +0000
Subject:Re: [TUHS] Archaic yacc C grammar

 Steve Johnson wrote:
 > Looking at the reserved words, there is one, ENTRY, that I've never
 > heard of (although FORTRAN had an ENTRY statement), and there is
 > STRUCT but no UNION. Also, he uses val= instead of $$=. There don't
 > seem to be any nontrivial assignment ops (neither += or =+).

 This is for Snyder's C compiler. There is something called =op which
 is guess is for =+ etc.

 > I'm guessing either Al wrote it from scratch or based it on some
other
 > similar program.

 Looks like you're right. I found this in another file, so it would
seem
 he wrote it back at MIT:

 "The original YACC was designed and implemented on a PDP-11/45 and a
 Honeywell 6000 by S. C. Johnson at Bell Laboratories. The version
 described in this paper was implemented on the PDP-10 by Alan Snyder.