OBJ is an algebraic specification language.

*** OBJ version of 99 bottles of beer
*** programmer: Grigore Rosu  grosu@cs.ucsd.edu
*** creator of OBJ language: Joseph Goguen

obj STRING is sort String .
  ops We like some beer on the wall.  : -> String .
  ops Take one bottle of wall down ,  : -> String .
  ops And pass it arround the beer.   : -> String .
  ops Does anybody want bottles more? : -> String .
endo

obj LIST[X :: TRIV] is
  sort List .
  subsort Elt < List .
  op __ : Li