|
Re: [xsl] XSLT repetition constructs
2019-03-08 14:24:01
Just one more interesting thing about the fold and scan functions --
yes, there is also a foldl-tree function:
One could specify compiling and running a program as a foldl() of
suitable argument functions.
Then, scanl() for the same functions will produce a full trace of the
run -- the results from each step in foldl(). This can be used for
debugging / verification.
We can imagine an XSLT 3.0+ processor written in a functional way, so
that running a transformation can be expressed as a foldl()
Then tracing/debugging this can be achieved simply by using scanl() .
Hopefully we can see such tools in our lives.
Cheers,
Dimitre
On Thu, Mar 7, 2019 at 7:18 AM Dimitre Novatchev
<dnovatchev(_at_)gmail(_dot_)com> wrote:
Yes, in Haskel there is a special function for this -- scanl
And this was implemented 15 years ago in FXSL:
Here is the code for f:scanl:
<xsl:stylesheet version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
xmlns:f="http://fxsl.sf.net/";
exclude-result-prefixes="f"
<xsl:import href="func-apply.xsl"/>
<xsl:function name="f:scanl">
<xsl:param name="pFunc" as="element()"/>
<xsl:param name="pA0"/>
<xsl:param name="pList" as="item()*"/>
<xsl:sequence select=
"$pA0,
(if (exists($pList))
then
f:scanl($pFunc,
f:apply($pFunc, $pA0, $pList[1]),
$pList[position() > 1]
)
else ()
)"
/>
</xsl:function>
<xsl:function name="f:scanl1">
<xsl:param name="pFun" as="element()"/>
<xsl:param name="pList" as="item()+"/>
<xsl:sequence select="f:scanl($pFun, $pList[1], $pList[position() > 1])"/>
</xsl:function>
</xsl:stylesheet>
And a test:
<xsl:stylesheet version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
xmlns:f="http://fxsl.sf.net/";
exclude-result-prefixes="f"
<xsl:import href="../f/func-scanl.xsl"/>
<xsl:import href="../f/func-Operators.xsl"/>
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:template match="/">
<xsl:value-of separator=", " select="f:scanl(f:add(), 0, /*/*)"/>
<xsl:text>
- - - - - - - - - - -
</xsl:text>
<xsl:value-of separator=", " select="f:scanl1(f:add(), /*/*)"/>
</xsl:template>
</xsl:stylesheet>
When this transformation is applied on this XML document:
<nums>
<num>01</num>
<num>02</num>
<num>03</num>
<num>04</num>
<num>05</num>
<num>06</num>
<num>07</num>
<num>08</num>
<num>09</num>
<num>10</num>
</nums>
the wanted result is produced:
0, 1, 3, 6, 10, 15, 21, 28, 36, 45, 55
- - - - - - - - - - -
01, 3, 6, 10, 15, 21, 28, 36, 45, 55
As an exercise one can code this in XPath 3.0
Cheers,
Dimitre
On Thu, Mar 7, 2019 at 5:27 AM Martin Honnen
martin(_dot_)honnen(_at_)gmx(_dot_)de
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
Am 07.03.2019 um 12:55 schrieb Michael Kay mike(_at_)saxonica(_dot_)com:
A good simple use case for fold-left() is to accumulate a running total,
i.e. turn (1,2,3,4) into (1,3,6,10).
The example to simply compute the running total (e.g. map (1,2,3,4) to
10) is in the spec with
fold-left((1 to 4), 0, function($a, $b) { $a + $b})
But to map the whole sequence (1,2,3,4) with fold-left to a new sequence
of (1,3,6,10) I am already struggling to express that in a compact way, is
fold-left(
(1 to 4),
(),
function ($a, $b) { $a, if (empty($a)) then $b else $b + $a[last()] }
)
a good way? Or can the third argument, the function be expressed in a
more compact way?
--
Cheers,
Dimitre Novatchev
---------------------------------------
Truly great madness cannot be achieved without significant intelligence.
---------------------------------------
To invent, you need a good imagination and a pile of junk
-------------------------------------
Never fight an inanimate object
-------------------------------------
To avoid situations in which you might make mistakes may be the
biggest mistake of all
------------------------------------
Quality means doing it right when no one is looking.
-------------------------------------
You've achieved success in your field when you don't know whether what
you're doing is work or play
-------------------------------------
To achieve the impossible dream, try going to sleep.
-------------------------------------
Facts do not cease to exist because they are ignored.
-------------------------------------
Typing monkeys will write all Shakespeare's works in 200yrs.Will they
write all patents, too? :)
-------------------------------------
Sanity is madness put to good use.
-------------------------------------
I finally figured out the only reason to be alive is to enjoy it.
--
Cheers,
Dimitre Novatchev
---------------------------------------
Truly great madness cannot be achieved without significant intelligence.
---------------------------------------
To invent, you need a good imagination and a pile of junk
-------------------------------------
Never fight an inanimate object
-------------------------------------
To avoid situations in which you might make mistakes may be the
biggest mistake of all
------------------------------------
Quality means doing it right when no one is looking.
-------------------------------------
You've achieved success in your field when you don't know whether what
you're doing is work or play
-------------------------------------
To achieve the impossible dream, try going to sleep.
-------------------------------------
Facts do not cease to exist because they are ignored.
-------------------------------------
Typing monkeys will write all Shakespeare's works in 200yrs.Will they
write all patents, too? :)
-------------------------------------
Sanity is madness put to good use.
-------------------------------------
I finally figured out the only reason to be alive is to enjoy it.
--~----------------------------------------------------------------
XSL-List info and archive: http://www.mulberrytech.com/xsl/xsl-list
EasyUnsubscribe: http://lists.mulberrytech.com/unsub/xsl-list/1167547
or by email: xsl-list-unsub(_at_)lists(_dot_)mulberrytech(_dot_)com
--~--
|
|