0 ▁series . ▁ ▁R PL ▁is ▁a ▁struct ured ▁programming ▁language ▁based ▁on ▁R PN , ▁but ▁equally ▁capable ▁of ▁processing ▁algebraic ▁expressions ▁and ▁formula e , ▁implemented ▁as ▁a ▁thread ed ▁interpreter . ▁R PL ▁has ▁many ▁similar ities ▁to ▁For th , ▁both ▁languages ▁being ▁stack - based , ▁as ▁well ▁as ▁the ▁list - based ▁L IS P . ▁Con tr ary ▁to ▁previous ▁H P ▁R PN ▁calcul ators , ▁which ▁had ▁a ▁fixed ▁four - level ▁stack , ▁the ▁stack ▁used ▁by ▁R PL ▁is ▁only ▁limited ▁by ▁available ▁calcul ator ▁RAM . ▁ ▁R PL ▁origin ated ▁from ▁H P ' s ▁Cor v all is , ▁Oregon ▁development ▁facility ▁in ▁ 1 9 8 4 ▁as ▁a ▁replacement ▁for ▁the ▁previous ▁practice ▁of ▁implementing ▁the ▁operating ▁systems ▁of ▁calcul ators ▁in ▁assembly ▁language . ▁The ▁last ▁pocket ▁calcul ator ▁supporting ▁R PL , ▁the ▁H P ▁ 5 0 g , ▁was ▁dis cont in ued ▁in ▁ 2 0 1 5 . ▁ ▁However , ▁ ▁multiple ▁em ul ators ▁that ▁can ▁em ulate ▁H P ' s ▁R PL ▁calcul ators ▁exist ▁that ▁run ▁on ▁a ▁range ▁of ▁operating ▁systems , ▁and ▁devices , ▁including ▁iOS ▁and ▁Android ▁smart ph ones . ▁ ▁Vari ants ▁The ▁internal ▁low - ▁to ▁medium - level ▁variant ▁of ▁R PL , ▁called ▁System ▁R PL ▁( or ▁S ys R PL ) ▁is ▁used ▁on ▁some ▁earlier ▁H P ▁calcul ators ▁as ▁well ▁as ▁the ▁a