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@xxxxxxxxx> 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], $pList[position() > 1])"/>
> </xsl:function>
> </xsl:stylesheet>
>
>
> And a test:
>
> <xsl:stylesheet version="2.0"
> xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
> xmlns:f="http://fxsl.sf.net/"
> exclude-result-prefixes="f"
> >
> <xsl:import href="../f/func-scanl.xsl"/>
> <xsl:import href="../f/func-Operators.xsl"/>
>
> <xsl:output omit-xml-declaration="yes" indent="yes"/>
>
> <xsl:template match="/">
> <xsl:value-of separator=", " select="f:scanl(f:add(), 0, /*/*)"/>
> <xsl:text>
- - - - - - - - - - -
</xsl:text>
> <xsl:value-of separator=", " select="f:scanl1(f:add(), /*/*)"/>
> </xsl:template>
> </xsl:stylesheet>
>
> When this transformation is applied on this XML document:
>
> <nums>
> <num>01</num>
> <num>02</num>
> <num>03</num>
> <num>04</num>
> <num>05</num>
> <num>06</num>
> <num>07</num>
> <num>08</num>
> <num>09</num>
> <num>10</num>
> </nums>
>
> the wanted result is produced:
>
> 0, 1, 3, 6, 10, 15, 21, 28, 36, 45, 55
> - - - - - - - - - - -
> 01, 3, 6, 10, 15, 21, 28, 36, 45, 55
>
> As an exercise one can code this in XPath 3.0
>
>
> Cheers,
> Dimitre
>
> On Thu, Mar 7, 2019 at 5:27 AM Martin Honnen martin.honnen@xxxxxx
> <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > Am 07.03.2019 um 12:55 schrieb Michael Kay mike@xxxxxxxxxxxx:
> > > A good simple use case for fold-left() is to accumulate a running total, i.e. turn (1,2,3,4) into (1,3,6,10).
> > >
> >
> > The example to simply compute the running total (e.g. map (1,2,3,4) to
> > 10) is in the spec with
> >
> > fold-left((1 to 4), 0, function($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.
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