denver

One of the sad things is that the MUMPS language specification was purportedly copyrighted; see <http://groups-beta.google.com/group/comp.lang.mumps/msg/f8f0d75dcc4c2860>.
The ANSI X11.1 specification should have most of what you want.

ed de moel

I am not aware that anyone ever published a BNF specification
of the M[UMPS] language. The standard has its own meta-language
diagrams, see e.g.
http://207.192.157.194/Demo/AnnoStd?...8&Edition=1995
but that language has no more than a seeming equivalence with
a BNF notation.

The MDC has made sevaral attempts to make the standards
documents available electronically. All these stranded on the
copyright restrictions of ANSI and ISO.

At the moment, all M[UMPS] related standards are available
on-line, be it in a piece-by-piece hypertext fashion.
The above-mentioned document can be reached from the start-page
at http://207.192.157.194/Demo/AnnoStd (which links through to
the various iterations of the standards documents, and includes
X11.1, X11.2, X11.3, X11.4 and X11.6 (indeed, there never was an
X11.5).

Hope this helps,
Ed