The Free On-line Dictionary of Computing (30 December 2018):

General Purpose Macro-generator
GPM

    (GPM) An early text-processing language similar to
   TRAC, implemented on the Atlas 2 by Christopher
   Strachey.

   ["A General Purpose Macrogenerator", C. Strachey, Computer J
   8(3):225-241, Oct 1965].

   (2006-07-21)