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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inport2,thethirdclausewillexecute;ifmessagesarriveatbothports, 10011.3.ControlFlowOperations<br />
thestatementwillblock. atinport1,thesecondclausewillexecute;ifamessagearrivesonlyat secondclausemaybeexecuted.Ifx0,thenif nomessageeverarrivesatinport1therstclausemusteventuallybe<br />
init.Thetypestateonentrytoanyclauseisthetypestateafterevaluatingallguards.Thetypestateonnormalterminationofthestatementis<br />
checkedtobeoftypefamilyinputport. sionsareinferredtobeoftypepredefined!boolean.Eventguardsare twoclauses. averagesalary,thenanon-deterministicchoiceismadebetweentherst behaveslikethechoicestatementsofotherlanguages.Iflowsalary= Allbooleanguards<strong>and</strong>alleventguardsmusthavetypestateattribute Herearethetype<strong>and</strong>typestatecheckingrules:Booleanguardexpres-<br />
Inthesecondexample,therearenoeventguards,<strong>and</strong>thestatement<br />
mally;ifnoneoftheclausescanexitnormally,thenneithercantheselect themeetofthetypestatesoncompletionofallclauseswhichcanexitnor-<br />
statement. ExpressionBlock<br />
able.Sinceexpressionsarenotsupposedtohavesideeects,allvariables clausecontainingstatementstocomputetheresultvariable. declaredoutsidetheexpressionblockareconstantwithintheblock. Anexpressionblock,orevaluateoperator,isawaytoembedstatements withinanexpression.Itcontainsadeclarationofaresultvariable,<strong>and</strong>a Theexpressionblockintroducesanewscopecontainingtheresultvari-<br />
secondary::=evaluatedeclarationfrom[statement;]...end<br />
normalexitfromtheblock.Itisa\deadcode"erroriftheclausedoesnot haveanormalexit.Theblockmustinitializetheresultvariable. Thetypestateafterexecutinganexpressionblockisthetypestateon forLispObjectinLispObjectswhere (evaluateStartsWithZ:booleanfrom blockbegin endblock; on(CaseError) revealLispObject.Pair; revealLispObject.Pair.Car.PrintName; StartsWithZ:=LispObject.Pair.Car.PrintName=Z; StartsWithZ:='false';
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