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Re: [xsl] What is the "closure" of a function?

Subject: Re: [xsl] What is the "closure" of a function?
From: "Abel Braaksma (Exselt) abel@xxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>
Date: Fri, 6 Jun 2014 11:39:36 -0000

On 23-5-2014 22:28, Dimitre Novatchev dnovatchev@xxxxxxxxx wrote:
>  The Functions and Operators 3.0 recommendation
> (http://www.w3.org/TR/xpath-functions-30/) uses the term "closure" of
> a function:
> "In effect, the static and dynamic part of the context thus act as
> part of the closure of the function item."
> However, there is no formal definition of "closure".
> A search for "closure " in the Data-Model 3.0" Recommendation yields 0 results.

It appears to me that at some point the term "closure" was dropped. In
the public 06/2011 version of the XDM, a definition existed:

"[Definition: The combination of the variable values needed to execute a
function and the function implementation are called a closure.]" (see

But in the following draft, 12/2011, this was dropped/revised.

It looks like the term closure was not fully removed in related documents.

> However, the XDM defines the so called "nonlocal variable bindings":
> "nonlocal variable bindings (a mapping from xs:QName to item()*): This
> provides a value for each of the function's free variables (i.e.,
> variables referenced by the function's implementation, other than
> locals and parameters)."
> My question is:
>   Is it safe to assume that what is referred to as the "closure"
> property of functions in the F & O document is the same as the
> "nonlocal variable bindings" property of functions, defined in the
> XDM?

Yes, I think that is a safe assumption.


Abel Braaksma
Exselt XSLT 3.0 streaming processor

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