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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eforebeinginsertedintoatableoftypeTmustbefinit(V),init(V.A), 8610.2.FormalTypestates<br />
variablename.Ifthevariablenameisabasevariablewithnocomponents, V.Theresultingtypestateiscalledaformaltypestate.Aformaltypestate itisreplacedby*.Theargumentlist(*)canoptionallybeomitted. lookslikeatypestate,exceptthatweomitthebasevariablefromeach init(V.B)g.Whenwewritethedenition,weomitthearbitraryvariable argumentofeachattribute,turningitfromavariablenameintoaformal ThedenitionsaysthatthetypestateofanarbitraryvariableVoftypeR T:tableofRfinit(*),init(A),init(B)gkeys(A);<br />
eachformalvariablenamewiththegivenvariablename. inwhichthetypeofthearbitraryvariableisknown. finit(X.Y),init(X.Y.A),init(X.Y.B)g.YoucansubstituteX.Yinto intotheformaltypestateinthedenitionabove,<strong>and</strong>obtainthetypestate ponentsofanarbitraryelementofatable. Tosubstituteavariablenameintoaformaltypestatemeanstoprex Aformalvariablenameorformaltypestateisalwayswritteninacontext Forexample,ifvariablenameX.YhastypeR,thenyoucansubstituteX.Y Formalvariablenamesarealsousedinkeylists,wheretheydenotecom-<br />
attributes,noteverycombinationofattributesisvalid. Becauseofthemeaningofthe<strong>Hermes</strong>datatypes<strong>and</strong>themeaningofthe 10.3ValidTypestates thekey<strong>and</strong>obtainanactualkeyofX.Y.A.<br />
tionsasinvalid: Herearetheattributecompatibilityruleswhichdenecertaincombina-<br />
Ifinit(X)isnotpresent,nootherattributewithargumentXmay<br />
Ifcase(V,V.A)ispresent,thennootherattributecase(V,V.B) IfXhascomponents,<strong>and</strong>init(X)isnotpresent,thennootherattributewithanycomponentasargumentmaybepresent.Thisfollows<br />
havevalues. fromthefactthatcomponentsofstructuredvaluesonlyexistwhen bepresent.Thisfollowsfromthefactthatonlyinitvariablescan thestructuredvalueitselfexists.<br />
Ifcase(V,V.A)ispresent,thenV.A'scasetypestateattributesare Ifcase(V,V.A)isabsent,thennootherattributewithV.Aascomponentmaybepresent.Thisfollowsfromthefactthatyoucanaccess<br />
componentsofavariantonlywhentheyarerevealed. variantexistsatatime. ispresent.Thisfollowsfromthefactthatonlyonecomponentofa present.ThesearetheattributesobtainedbysubstitutingV.Ainto
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