Hermes: A Tutorial and Reference Manual - Researcher - IBM
Hermes: A Tutorial and Reference Manual - Researcher - IBM
Hermes: A Tutorial and Reference Manual - Researcher - IBM
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152B.1.OperationDescriptions inferthetypeoftheleft-h<strong>and</strong>oper<strong>and</strong>,ifeithertheruleisoftheassignment variety,orifthetypeoftheright-h<strong>and</strong>oper<strong>and</strong>isalreadyknown. Aninferencerulecanbeusedfortypechecking.Itcanalsobeusedto<br />
ofeitheroper<strong>and</strong>canbeinferredfromthetypeoftheother. fromthemergeatoperation: tion,whichidentiestwooper<strong>and</strong>sthatmusthavethesametype.Allsuch rulesinanoperationdescriptionaredisplayedasinthefollowingexample Inthiscase,thenormalasymmetryofinferencerulesvanishes:thetype Aspecialnotationisusedforrulesinvolvingthesameasinferencefunc-<br />
B.1.3Preconditions Precondition<strong>and</strong>postconditionrulesappearinside-by-sideboxesbelow thetyperules. destinationsource<br />
timetheoperationistobeexecuted.Allpreconditionsmustbestatically veriablebythecompiler. Thepreconditionrulesspecifyvariousconditionsthatmustholdatthe<br />
deneconditionsunderwhichanexceptionisknowntobepossible.Forexample,thefollowingpreconditionindicatesthatifthedestinationoper<strong>and</strong><br />
isakeyedtable,thentheoperationcanraiseDuplicateKey: init(source) operationcantakeplace. listofoper<strong>and</strong>s.Anexamplefromthemergeatoperationis: Some\preconditions"donotcheckforanytypestateattributes.They Thisstatesthatthesourceoper<strong>and</strong>mustbeinitializedbeforethemergeat Apreconditiontakestheformofapreconditionfunctionfollowedbya<br />
B.4. B.1.4Postconditions Thepostconditionrulescharacterizetheeectsofanormal(non-exception) executionoftheoperation.Eachruleisspeciedviaapostconditionfunctionfollowedbyalistofoper<strong>and</strong>s.Anexamplefromthemergeatoperation<br />
is: Allthepreconditionfunctions<strong>and</strong>theirmeaningsarelistedinsection duplicatekey(destination)<br />
makeuninit(source)
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