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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isconcerned.Allthe\noisewords",likeof,from<strong>and</strong>into,whichmakethe <strong>Hermes</strong>programvalue.Thisisamuchsimplerformasfarasthecomputer Afteramodulehasbeentokenized,parsed,<strong>and</strong>resolved,itisstoredasa 9TypeChecking<strong>and</strong>Inference programeasierforpeopletoreadbutlesssyntacticallyregular,aregone. Statementswithembeddedexpressionsareexp<strong>and</strong>edouttosequencesof statements.Names,likeX,whoseresolutionmaybecontext-sensitive,have beenremoved.Intheirplaceareuniqueidentiers. clauseisaseriesofstatements,<strong>and</strong>eachstatementisanoperator,alistof oper<strong>and</strong>s(variablenames),<strong>and</strong>a\qualier",whichiseverythingelse.By ofdeclarations,organizedinto\scopes";(3)acollectionofclauses.Each constraintdenitions,organizedintodenitionsmodules;(2)acollection declared. thistime,allbasevariablenamesexceptexpressiontemporarieshavebeen The<strong>Hermes</strong>programvalueis:(1)acollectionoftypedenitions<strong>and</strong><br />
inferencerulesareusedforbothinference<strong>and</strong>checking.Theclassrulesare rules.Therearetwofamiliesofrules:inferencerules,<strong>and</strong>classrules.The typesoftheoper<strong>and</strong>s. theexpressiontemporariessothateverybasevariablewillhaveaknown type;(2)typechecking:tocheckthattheoperationsarelegal,giventhe anextrasetofcheckswhichapplyaftertypeinferenceiscomplete. Bothtypeinference<strong>and</strong>typecheckingaredrivenfromasingletableof Thejobofthenextphaseis:(1)typeinference:tosupplydeclarationsfor<br />
thetypeoftheoper<strong>and</strong>ontheleft. theleft.Thesecondkindofruleisredwhenthetypeoftheoper<strong>and</strong>on therightbecomesknown.Theruleprovidesafunctionwhichdetermines inferencerule:oper<strong>and</strong> Therstkindofruleunconditionallyassignsatypetotheoper<strong>and</strong>on Therulesappearintheappendix.Thesyntaxofaninferenceruleis:<br />
insertat(table,element,position)absent Thetyperulesinthetableentryforthisoperationlooklikethis:<br />
rulename()<br />
table2orderedtable rulename(oper<strong>and</strong>)<br />
tointherulesastable,element,<strong>and</strong>position.Thereisnoqualier.The thattheoperationinsertathasthreeoper<strong>and</strong>s,whichwillbereferred Forexample,let'slookattheoperationinsertat.Theheaderlinestates<br />
element elementtypeof(table) predefinedinteger()
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