for ement ioned ▁ones , ▁as ▁part ▁of ▁their ▁operating ▁system ▁implementation ▁language . ▁ ▁In ▁the ▁H P   4 8 ▁series ▁this ▁variant ▁of ▁R PL ▁is ▁not ▁accessible ▁to ▁the ▁calcul ator ▁user ▁without ▁the ▁use ▁of ▁external ▁tools , ▁but ▁in ▁the ▁H P   4 9 / 5 0 ▁series ▁there ▁is ▁a ▁compiler ▁built ▁into ▁R OM ▁to ▁use ▁S ys R PL . ▁It ▁is ▁possible ▁to ▁cause ▁a ▁serious ▁crash ▁while ▁coding ▁in ▁S ys R PL , ▁so ▁ca ution ▁must ▁be ▁used ▁while ▁using ▁it . ▁ ▁The ▁high - level ▁User ▁R PL ▁( or ▁User R PL ) ▁version ▁of ▁the ▁language ▁is ▁available ▁on ▁said ▁graph ing ▁calcul ators ▁for ▁developing ▁text ual ▁as ▁well ▁as ▁graph ical ▁application ▁programs . ▁ ▁All ▁User R PL ▁programs ▁are ▁internally ▁represented ▁as ▁S ys R PL ▁programs , ▁but ▁use ▁only ▁a ▁safe ▁subset ▁of ▁the ▁available ▁S ys R PL ▁commands . ▁ ▁The ▁error ▁checking ▁that ▁is ▁a ▁part ▁of ▁User R PL ▁commands , ▁however , ▁makes ▁User R PL ▁programs ▁notice ably ▁slower ▁than ▁equivalent ▁S ys R PL ▁programs . ▁The ▁User R PL ▁command ▁SY SE VAL ▁tells ▁the ▁calcul ator ▁to ▁process ▁designated ▁parts ▁of ▁a ▁User R PL ▁program ▁as ▁S ys R PL ▁code . ▁ ▁Control ▁blocks ▁R PL ▁control ▁blocks ▁are ▁not ▁strictly ▁post fix . ▁ ▁Although ▁there ▁are ▁some ▁notable ▁exceptions , ▁the ▁control ▁block ▁structures ▁appear ▁as