[xquery-talk] :=

[Benito van der Zander]

Hi,

>    You may find some resources that somewhat misleadingly define ":="
> as the "assignment operator," a phrase that is not found in any XQuery
> or XPath specification. Calling ":=" the "assignment operator" is
> incorrect in two respects. First, ":=" is involved in the *binding*,
> not *assigning*, of values to variables—an important distinction in
> functional and declarative languages like XQuery, in which a variable,
> once bound to a value, cannot be altered, or reassigned a different
> value. Second, the ":=" cannot be described as an *operator* because
> it does not produce an output sequence of items, in contrast to
> operators like "+" (an arithmetic operator), "and" (a boolean
> operator), and "/" (an operator for connecting steps in a path
> expression).


although some implementations have a scripting extensions, where there 
actually is an assignment operator, which does both these things.



Cheers,
Benito



On 11/21/2016 06:40 PM, Joe Wicentowski wrote:
> Hi Ghislain,
>
> Thanks very much for your reply!  If ":=" is not an "operator," by
> your helpful definition, then is there a category like "symbol,"
> "delimiter," or at worst, "thingy," that it *does* rightly belong to?
> I'm looking to fill in the blank in the following sentence, which
> builds on your summary:
>
>    ":=" has no formal name in the XPath and XQuery specifications but
> is used extensively in clauses and declarations that bind variables.
> Specifically, it is used in let and group-by clauses (which produce
> tuples) as well as variable and context item declarations (which
> contribute to the dynamic context). Rather than leaving this important
> symbol nameless, let's call it the "binding ____."
>
> I'm also thinking of a parenthetical note or footnote like this:
>
>    You may find some resources that somewhat misleadingly define ":="
> as the "assignment operator," a phrase that is not found in any XQuery
> or XPath specification. Calling ":=" the "assignment operator" is
> incorrect in two respects. First, ":=" is involved in the *binding*,
> not *assigning*, of values to variables—an important distinction in
> functional and declarative languages like XQuery, in which a variable,
> once bound to a value, cannot be altered, or reassigned a different
> value. Second, the ":=" cannot be described as an *operator* because
> it does not produce an output sequence of items, in contrast to
> operators like "+" (an arithmetic operator), "and" (a boolean
> operator), and "/" (an operator for connecting steps in a path
> expression).
>
> (For some resources that use the term "assignment operator," see via
> https://www.google.com/search?q=%22assignment+operator%22+xquery.)
>
> It's funny, "/" didn't have a name in XPath 1.0, but got one in XPath
> 3.0 - "path operator."  Perhaps it's time for ":=" to get a name?
>
> Thanks again,
> Joe
>
>> Syntactically, ":=" is not an operator because it does not produce an output
>> sequence of items like "+" or "and" or "/". It is part of let and group-by
>> clauses (which produce tuples) as well as variable and context item
>> declarations (which contribute to the dynamic context).
>>
>>  From a pedagogical perspective, I would simply call it a variable binding,
>> the important part being not to call it "assignment" to make clear that it
>> is a functional and declarative language.
> _______________________________________________
> talk at x-query.com
> http://x-query.com/mailman/listinfo/talk

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://x-query.com/pipermail/talk/attachments/20161121/b7016761/attachment.html>