[Bug 5747] [FS] Expansion of castable throws errors

http://www.w3.org/Bugs/Public/show_bug.cgi?id=5747





--- Comment #3 from Michael Dyck <jmdyck@ibiblio.org>  2008-07-05 08:53:10 ---
For 4.12.4 Castable, I think the Dynamic Evaluation rules should be:

    dynEnv |- Expr => Value
    Value can be cast to SingleType
    ----------------------
    dynEnv |- Expr castable as SingleType => true

    dynEnv |- Expr => Value
    not( Value can be cast to SingleType )
    ----------------------
    dynEnv |- Expr castable as SingleType => false

where the auxiliary judgment "Value can be cast to SingleType" is defined by
the following rules:

    --------------
    () can be cast to AtomicType?

    Value can be cast to AtomicType
    --------------
    Value can be cast to AtomicType?

    fn:data(Value) = AtomicValue1
    AtomicValue1 cast value to type AtomicType => AtomicValue2
    --------------
    Value can be cast to AtomicType


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