Hermes: A Tutorial and Reference Manual - Researcher - IBM

1.2GettingStarted|ASimpleHermesProgram another.Thereissomecost:youhavetowritemoredeclarations. thoughsomeprogramsmayhavebugsandtheusersdon'ttrustone 1.IntroductiontoHermes5
Let'sstartwithourrstHermesprogram. siblytypedenitions.We'llshowyouinalatersectionhowtowritethem. receiveParmsfromInit;
Pascal Let'sassumefornowthatyouhavealreadywrittenthemorthattheyhave alreadybeensuppliedforyou. doesitdierfromthecorrespondingprograminC,Ada([SYW85]),or Beforeyoucompilethisprogram,youhavetoadddeclarationsandpos-
ThisprogramcanbeusedtodisplaythemessageHello,World!.How callParms.PutLine("Hello,World!"); returnParms;
PutLine.InHermes,PutLineisaparameter;itscounterpartsintheother languagesareconstants. mesversionofthissimpleprogramandalltheothers|thelatebindingof syntax,thereisneverthelessanimportantdistinctionbetweentheHer-
Althoughatrstglancetheprogramsappeartodieronlyinsupercial write("Hello,World!")fAPascalprogramg printf("Hello,World!");/*aCprogramtodotheabove*/
IntheCprogram,printfhasaxedbinding|itdenotesalibraryprogramwhichwritesthecharacterstringtothestandardoutput.Theonly
Ifyoudothis,youwillalsochangethebindingofprintfforallthemod-
([KR78]),functionsarenotvariables.Ifyouwanttocontrolthebindingof ulesofyourprogram.TousetheterminologyoftheCreferencemanual afunctionwithaCprogram,youmustsimulatefunctionvariablesusing pointerstofunctions.(SimilarlyinPascal([Coo83])andAda,functionsare notvariables.Intheselanguagesthereisawaytoachievealimiteddegree ofdynamicbinding.) ofHermes:(1)nothingisglobal,and(2)everyfunctionorprocedurename referstoavariablewhosevalueisdeterminedatrun-time,notcompiletime.
asParms.PutLine.Hermesisdesignedthiswaybecauseitassumesyou receivetheparameterlistParmsandbecausewemustrefertothefunction SoeveninthistinyHermesprogram,youcanseetwoimportantfeatures
PUT("Hello,World!")--AnADAprogram
waytochangethebindingistolinkyourCprogramtoadierentlibrary.
WhydowedothisAfterall,theprogramislongerbecausewemust