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XSLT 2.0 Issue 104: Arity Overloading instead of Parameter Defaul ting for xsl:function

From: Bohlmann, Karsten <karsten.bohlmann@sap.com>
Date: Mon, 15 Apr 2002 06:40:23 -0400 (EDT)
Message-ID: <67B8CED503F3D511BB9F0008C75DAD660E544E@dbwdfx17.wdf.sap-ag.de>
To: "'xsl-editors@w3.org'" <xsl-editors@w3.org>
Hi,

I would like to bring forward an argument against optional arguments for
functions defined with xsl:function.

Optional arguments are, in my opinion, an improper transfer of the
xsl:call-template logic. Templates have name parameters, while functions
have positional parameters. It makes perfect sense to have value defaulting
for named parameters. But for positional parameters, it's rather a source of
confusion.

It's more useful, and less error-prone, to allow overloading of function
names. In our case, overloading only concerns the arity. Thus, I suggest to
allow multiple function definitions F/n with the same name F, but differing
in the number n of formal parameters. F(e_1,...,e_n) is then a static error
if no function F/n is defined. (Or, in the spirit of XSLT 1.0 regulations, a
dynamic error.)

Consequently, the default-value part of xsl:param would become redundant.
Therefore, it might be a good idea to use a different sub-instruction to
xsl:function, xsl:argument, which merely specifies the formal parameter
name.

The mechanism of default parameters can be easily simulated with function
overloading:

<xsl:function name="p:f"> <!-- 0/1-ary -->
  <xsl:param name="x" select="42"/>
  <xsl:return select="p:g($x)+p:h($x)"/>
</xsl:function>

becomes

<xsl:function name="p:f"> <!-- 1-ary -->
  <xsl:argument name="x"/>
  <xsl:return select="p:g($x)+p:h($x)"/>
</xsl:function>
<xsl:function name="p:f"> <!-- 0-ary -->
  <xsl:return select="p:f(42)"/>
</xsl:function>

However, frequently F/n is related to F/(n+k) in a more sophisticated way
(or not at all):

<xsl:function name="p:f"> <!-- 0-ary (alternative) -->
  <xsl:return select="if @a then p:f(@a) else p:g(@b)"/>
</xsl:function>

Showing that overloading is more general than parameter defaulting.


Best regards,

Karsten Bohlmann

Server Infrastructure Technology
SAP AG
Received on Monday, 15 April 2002 08:26:00 GMT

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