Re: [xsl] Functional program for "list sum"

[Dimitre Novatchev <dnovatchev@xxxxxxxxx>]

On 6/10/05, Mukul Gandhi <mukul_gandhi@xxxxxxxxx> wrote:
> Hello Dimitre,
>  Can I hope to get response from you ..
>
> Regards,
> Mukul

Hi Mukul,

There are good books on Functional programming and I am not at all an
authority in this field.

If you really need to look at what I've written on this subject (in
relation to FXSL), one source is available at:

   http://www.mulberrytech.com/Extreme/Proceedings/xslfo-pdf/2003/Novatchev01
/EML2003Novatchev01.pdf


As for an example of a function that calculates the sum of the
elements of a list, do have a look at how this is done in FXSL.

As one might have expected, this is a simple application of the foldl
function, which in Haskell can be written as:

sum xs   =  foldl (+) 0 xs


Now, as an exercise, think how to define a function that calculates
the product of all elements of a list  :o)

Here's the defiition of f:sum() from FXSL:

<xsl:stylesheet version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
xmlns:xs="http://www.w3.org/2001/XMLSchema";
xmlns:f="http://fxsl.sf.net/";
xmlns:sum-fold-func="sum-fold-func"
exclude-result-prefixes="f xs sum-fold-func"
>
   <xsl:import href="func-foldl.xsl"/>

    <xsl:function name="f:sum">
      <xsl:param name="pList"/>

      <xsl:variable name="sum-fold-func"
                    select="document('')/*/sum-fold-func:*[1]"/>

      <xsl:sequence select="f:foldl($sum-fold-func, 0, $pList)"/>
    </xsl:function>

    <sum-fold-func:sum-fold-func/>
    <xsl:template name="add" match="sum-fold-func:*"
     mode="f:FXSL">
         <xsl:param name="arg1" select="0"/>
         <xsl:param name="arg2" select="0"/>

         <xsl:value-of select="$arg1 + $arg2"/>
    </xsl:template>

</xsl:stylesheet>


Cheers,
Dimitre Novatchev





> -------------------------------------------------
> "Two parallel lines touch each other at infinity"
> -------------------------------------------------
>
> --- Mukul Gandhi <mukul_gandhi@xxxxxxxxx> wrote:
>
> > I am trying to implement a "integer sum" function in
> > a
> > functional manner .. My stylesheet so far is -
> >
> > <?xml version="1.0"?>
> > <xsl:stylesheet
> > xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
> >
> > xmlns:xs="http://www.w3.org/2001/XMLSchema";
> >                 xmlns:fn="http://whatever";
> >                 version="1.0">
> >
> >  <xsl:output method="text" />
> >
> >  <xsl:template match="/">
> >     <xsl:variable name="result"
> > select="fn:listSum(null,(1,2,3))" />
> >     <xsl:value-of select="$result" />
> >  </xsl:template>
> >
> >  <xsl:function name="fn:listSum" as="xs:integer">
> >     <xsl:param name="num" as="xs:integer" />
> >     <xsl:param name="list" as="xs:integer+" />
> >     <xsl:sequence
> > select="fn:listSum($num,$list[position() &gt; 1])"
> > />
> >  </xsl:function>
> >
> > </xsl:stylesheet>
> >
> > But I am getting following error with Saxon 8.4 ..
> >
> > "Warning: Running an XSLT 1.0 stylesheet with an
> > XSLT
> > 2.0 processor
> > Error on line 10 of file:/C:/xml/xsleg/xslt/fp.xsl:
> >   XPTY0004: An empty sequence is not allowed as the
> > first argument of fn:listSum
> > ()
> > Transformation failed: Run-time errors were
> > reported"
> > ..
> >
> > Can someone please help me ..?
> >
> > Regards,
> > Mukul
> >
> >
> >
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