I'm having a hard time dealing with boolean values in variables, and
i'm not sure if the approach i'm taking is possible/sensible.  As far
as i understand, the xpath boolean() function should return false for
the empty string, 0, boolean false and the empty node-set; and true
for all other values.  I want to be able to store values in a
variable, and then test the variable in a xsl:if, but it always
evaluates to true.  Here is a small test file, which shows the
different methods i've tried.  None of them work!

<?xml version="1.0"?>
<xsl:stylesheet
   xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
   version="1.0">

   <xsl:template match="/">
       <xsl:variable name="true">
           <xsl:call-template name="get-true"/>
       </xsl:variable>

       <xsl:variable name="false">
           <xsl:call-template name="get-false"/>
       </xsl:variable>

       Test1:
       <xsl:call-template name="boolean-check">
           <xsl:with-param name="var" select="$true"/>
       </xsl:call-template>

       <xsl:call-template name="boolean-check">
           <xsl:with-param name="var" select="$false"/>
       </xsl:call-template>

       Test2:
       <xsl:call-template name="boolean-check2">
           <xsl:with-param name="var" select="$true"/>
       </xsl:call-template>

       <xsl:call-template name="boolean-check2">
           <xsl:with-param name="var" select="$false"/>
       </xsl:call-template>

       Test3:
       <xsl:call-template name="boolean-check3">
           <xsl:with-param name="var" select="$true"/>
       </xsl:call-template>

       <xsl:call-template name="boolean-check3">
           <xsl:with-param name="var" select="$false"/>
       </xsl:call-template>

   <xsl:template name="boolean-check">
       <xsl:param name="var"/>

       <xsl:choose>
           <xsl:when test="$var">
               Variable is true
           </xsl:when>
           <xsl:otherwise>
               Variable is false
           </xsl:otherwise>
       </xsl:choose>
   </xsl:template>

   <xsl:template name="boolean-check2">
       <xsl:param name="var"/>

       <xsl:choose>
           <xsl:when test="boolean($var)">
               Variable is true
           </xsl:when>
           <xsl:otherwise>
               Variable is false
           </xsl:otherwise>
       </xsl:choose>

   <xsl:template name="boolean-check3">
       <xsl:param name="var"/>

       <xsl:choose>
           <xsl:when test="$var = true()">
               Variable is true
           </xsl:when>
           <xsl:otherwise>
               Variable is false
           </xsl:otherwise>
       </xsl:choose>

   <xsl:template name="get-true">
       <xsl:value-of select="true()"/>
   </xsl:template>

   <xsl:template name="get-false">
       <xsl:value-of select="false()"/>
   </xsl:template>

I'm getting the feeling that i've seriously missed the point somewhere
along the line, could anyone explain why this code fails, and the
proper way to deal with booleans in variables?