4.1.5 Function Calls

Notation
[]_FunctionArgument
    First, picking up on Bug 1576 comment #2, note that the conditional
    structures of []_AtomizeAtomic and []_Convert are now identical,
    so the two can be merged (into []_ConvertAtomic, say):

        [ Expr ]_ConvertAtomic(SequenceType) denotes
        fs:convert-simple-operand(fn:data(Expr),PrototypicalValue)
            If [SequenceType]_sequencetype <: xdt:anyAtomicType*
        Expr
            Otherwise

    Second, note that, as seen at the end of Bug 1680 comment #4,
    []_FunctionArgument() is actually invoked with a Type, not a
    SequenceType (because when you look up the function name/arity in
    statEnv.funcType, you get a signature with Types, not SequenceTypes).
    This modifies the above definition to:

        [ Expr ]_ConvertAtomic(Type) denotes
        fs:convert-simple-operand(fn:data(Expr),PrototypicalValue)
            If Type <: xdt:anyAtomicType*
        Expr
            Otherwise

    Finally, I suggest that rather than using this ad hoc If/Otherwise
    notation, the whole []_FunctionArgument() mapping would be better
    expressed as two inference rules:

        statEnv |- Type <: xdt:anyAtomicType*
        -------------------------------------
        statEnv |- [ Expr ]_FunctionArgument(Type) =
            fs:convert-simple-operand(fn:data( [Expr]_Expr ),ProtoValue)

        statEnv |- not( Type <: xdt:anyAtomicType* )
        --------------------------------------------
        statEnv |- [ Expr ]_FunctionArgument(Type) = [Expr]_Expr