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RE: Re: mapping (Was: Re: Re: . in for)

Subject: RE: Re: mapping (Was: Re: Re: . in for)
From: Dimitre Novatchev <dnovatchev@xxxxxxxxx>
Date: Wed, 9 Jan 2002 05:25:16 -0800 (PST)
sumproducts function
"Michael Kay" <michael dot h dot kay at ntlworld dot com> wrote:

> > As I already pointed out in my reply to Dave,
> >
> > >   $departments map lower-case(.)
> >
> > would be ambiguous, as lower-case(.) is a value/string (the
> > result of the
> > application of lower-case() on .
> >
> 
> Actually this syntax is perfectly feasible technically, and isn't far off
> from something I myself proposed at one stage. Given that the data model
> doesn't currently allow functions or expressions as operands to a function,
> all higher-order functionality in XPath 2.0 is currently expressed using
> operators that are built into the language. For example E1/E2 and E1[E2] are
> both higher-order constructs where E2 is evaluated once for each item in E1,
> and it would be quite feasible for (E1 map E2) to work the same way - if
> that's how the WG decided to go. 

The same semantics can be expressed using different syntactic constructs. I am
following the Haskell style, in which brackets and arguments are omitted, if
possible.

This results in a considerably more compact and readable expressions.

For example, which of the two function definitions is more readable and
understandable:

sumProducts($seq) = sum(map(product(), $seq))

or

sumProduct = sum . (map product)

> The last time it was debated, we decided
> not to go there (Query folks are very attached to their FLWR expressions and
> regard this construct as redundant): but a good argument would still receive
> a hearing.

It seems that the balance is unproportionally shifted towards the Query folks. Why
should this be so? Why it would not be the other way around:

"The last time it was debated, we decided
not to go there (XSLT folks are very attached to their higher-order functions and
regard "the XXX construct" as redundant): but a good argument would still receive
a hearing."

Cheers,
Dimitre Novatchev.




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