programming ▁language ▁but ▁is ▁intended ▁for ▁teaching ▁or ▁pro tot yp ing . ▁ ▁The ▁language ▁had ▁a ▁major ▁influence ▁on ▁the ▁design ▁of ▁the ▁Python ▁programming ▁language ; ▁Gu ido ▁van ▁Ros sum , ▁who ▁developed ▁Python , ▁previously ▁worked ▁for ▁several ▁years ▁on ▁the ▁ABC ▁system ▁in ▁the ▁mid ▁ 1 9 8 0 s . ▁ ▁Fe atures ▁Its ▁design ers ▁claim ▁that ▁ABC ▁programs ▁are ▁typically ▁around ▁a ▁quarter ▁the ▁size ▁of ▁the ▁equivalent ▁Pascal ▁or ▁C ▁programs , ▁and ▁more ▁readable . ▁Key ▁features ▁include : ▁ ▁Only ▁five ▁basic ▁data ▁types . ▁Does ▁not ▁require ▁variable ▁declarations . ▁Exp licit ▁support ▁for ▁top - down ▁programming . ▁Stat ement ▁nest ing ▁is ▁indicated ▁by ▁ind entation , ▁via ▁the ▁off - side ▁rule . ▁In finite ▁precision ▁arithmetic , ▁un limited - s ized ▁lists ▁and ▁strings , ▁and ▁other ▁features ▁supporting ▁orth og on ality ▁and ▁ease ▁of ▁use ▁by ▁nov ices . ▁ ▁ABC ▁was ▁originally ▁a ▁mon ol ith ic ▁implementation , ▁leading ▁to ▁an ▁in ability ▁to ▁adapt ▁to ▁new ▁requirements , ▁such ▁as ▁creating ▁a ▁graph ical ▁user ▁interface . ▁ABC ▁could ▁not ▁directly ▁access ▁the ▁underlying ▁file ▁system ▁and ▁operating ▁system . ▁ ▁The ▁full ▁ABC ▁system ▁includes ▁a ▁programming ▁environment ▁with ▁syntax - direct ed ▁editing , ▁suggestions , ▁persistent ▁variables , ▁and ▁multiple ▁work spaces ▁- ▁and ▁is ▁available ▁as ▁an ▁interpreter / compiler , ▁currently ▁at ▁version ▁ 1 . 0 5 . 0 2 , ▁and ▁port