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

HPL

   Language used in HP9825A/S/T "Desktop Calculators", 1978(?)
   and ported to the early Series 200 family (9826 and 9836,
   68000).  Fairly simple and standard, but with extensive I/O
   support for data acquisition and control (BCD, Serial, 16 bit
   custom and IEEE 488 interfaces), including interrupt
   handling.  Currently owned by Structured Software Systems.
   "HPL Operating Manual for Series 200, Models 216, 226 and
   235\6", HP 98614-90010, Jan 1984.