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[Bug 29586] [XQ31] 2.5.6.2 The judgement subtype-itemtype(Ai, Bi)

From: <bugzilla@jessica.w3.org>
Date: Tue, 03 May 2016 09:47:26 +0000
To: public-qt-comments@w3.org
Message-ID: <bug-29586-523-2HY01mICW6@http.www.w3.org/Bugs/Public/>
https://www.w3.org/Bugs/Public/show_bug.cgi?id=29586

John Snelson <john.snelson@marklogic.com> changed:

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--- Comment #5 from John Snelson <john.snelson@marklogic.com> ---
I agree with Michael Kay - this is a deliberate design decision. In fact,
things break if a map type can be a subtype of a function type - as I described
in the email referenced.

It may help to think of it like this: The map interface doesn't inherit from
the function interface - however all map instances (objects) implement both the
map and the function interface.

>From a static typing perspective, it's as if an expression that returns a map
has two equally valid static types - it's returning a value that is both a map
and a function. Implement that as you will, since we aren't standardizing
static typing any more.

You need to remember that the type system isn't defined by the SequenceType
syntax. That syntax only defines the types you can test for in the language,
and what it means to pass or fail those tests.

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