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

WonderPop
WPOP

    (WPOP) An implementation of POP for the PDP-10
   made by Robert Rae  in Edinburgh in 1976.
   WonderPop used "cages" for different data types and
   introduced processes, properties and some typed
   identifiers.

   (2016-12-24)