Hermes: A Tutorial and Reference Manual - Researcher - IBM

ments.Therstargumenttocasemustbeavariantvariable,andthesecondmustbeacomponentofthesamevariantvariable.Attributechecked
musthaveasingleargumentoftypepredefined!program.Attribute definitionsmodule. checkeddefinitionsmusthaveasingleargumentoftypepredefined! Allotherattributenamesareconstraintattributes.Whenyoumention 10.TypestateChecking85
howmanyattributeargumentstheremustbeandwhatthetypeofeach aconstraintattribute,therewillbeaconstraintdenitionwhichspecies mustbe. Forexample,ifthereisaconstraintdenition greaterthan:constraint(a:integer,b:integer)IS
thisuseasanabbreviation,youmaynotdeneanattributenamedfull. X.AofX.Forothertypes,fullmeansthesameasinit.Fromnowon, we'llassumefullhasbeenexpandedoutwhereveritappears.Becauseof it'sthesameasifyouwroteinit(X)andfull(X.A)foreachcomponent abbreviation.Ifyouwritefull(X),andXisarecordorcallmessage,then argumentsoftypeinteger. thentheattributegreaterthanmustalwaysappearwithexactlytwo Thenamefullissyntacticallyanattributename,butitistreatedasan finit(a),init(b)ga>b;
Herearethemeaningsofthetypestateattributes: checked(P)meansthatprogramPhasbeencheckedandisfreeof case(V,V.X)meansthatvariantVisrevealed,andcomponentV.X init(X)meansthevariableXisinitialized;otherwiseitisuninitialized.
exists;theabsenceofcase(V,...)meansthatvariantVishidden. syntaxerrors,includingresolutionerrors,typeerrors,andtypestate checkedandassignedauniquename.(Seethediscussionofthecheckdefinitions errors. checkeddefinition(D)meansthatdenitionsmoduleDhasbeen
10.2FormalTypestates attributename(arguments)meansthatthenamedconstraintpredicateisknowntobetrueofitsarguments.
statement.)
Sometimesatypestatemustbewrittenwithoutthebasevariables.For example,hereisthedenitionofarecord,andatableoftheserecords: R:record(A:integer,B:Charstring);