Re: What is the "closure" of a function?

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
http://www.w3.org/TR/2011/WD-xpath-datamodel-30-20110614/#function-items)

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.

Cheers,

Abel Braaksma
Exselt XSLT 3.0 streaming processor
http://exselt.net