<?xml-stylesheethref="eight-queens.xsl" type="text/xsl"?>
-<o:program>
 <o:param name="servlet:req"/>
<!--
 This example implements a solution to the Eight Queens Problem,
       how to place eight queens on a chess board in such a way that
       no one queen threatens (is on the diagonal or straight line of)
       any other
 -->
<!--
 define our types: Queen and QueenSolver
 -->
-<o:type name="ex:Queen">
 <o:variable name="row" select="1"/>
 <o:variable name="column"/>
 <o:variable name="neighbour"/>
-<o:function name="ex:Queen">
<!--
 type constructor
 -->
 <o:param name="column" type="Number"/>
 <o:param name="neighbour"/>
<!--
 column and neighbour are automatically set from their parameter
 -->
<!--
 values, row is set from default value
 -->
-<o:do>
 <o:set row="1"/>
 </o:do>
 </o:function>
-<o:function name="findSolution">
-<o:do>
-<o:while test="$neighbour and $neighbour.canAttach($row, $column)">
-<o:if test="not($this.advance())">
 <o:return select="false()"/>
 </o:if>
 </o:while>
 <o:return select="true()"/>
 </o:do>
 </o:function>
-<o:function name="advance">
-<o:do>
-<o:choose>
-<o:when test="$row < 8">
 <o:set row="$row + 1"/>
 <o:return select="$this.findSolution()"/>
 </o:when>
-<o:when test="$neighbour">
-<o:if test="not($neighbour.advance())">
 <o:return select="false()"/>
 </o:if>
-<o:if test="not($neighbour.findSolution())">
 <o:return select="false()"/>
 </o:if>
 </o:when>
-<o:otherwise>
 <o:return select="false()"/>
 </o:otherwise>
 </o:choose>
 <o:set row="1"/>
 <o:return select="$this.findSolution()"/>
 </o:do>
 </o:function>
-<o:function name="canAttach">
 <o:param name="testRow"/>
 <o:param name="testColumn"/>
-<o:do>
 <o:variable name="columnDifference" select="$testColumn - $column"/>
-<o:choose>
-<o:when test="$row = $testRow or ($row + $columnDifference = $testRow) or ($row - $columnDifference = $testRow)">
 <o:return select="true()"/>
 </o:when>
-<o:when test="$neighbour">
 <o:return select="$neighbour.canAttach($testRow, $testColumn)"/>
 </o:when>
 </o:choose>
 <o:return select="false()"/>
 </o:do>
 </o:function>
-<o:function name="paint">
-<o:do>
-<o:if test="$neighbour">
 <o:eval select="$neighbour.paint()"/>
 </o:if>
-<queen>
-<column>
 <o:eval select="$column"/>
 </column>
-<row>
 <o:eval select="$row"/>
 </row>
 </queen>
 </o:do>
 </o:function>
 </o:type>
-<o:type name="ex:QueenSolver">
 <o:variable name="lastQueen"/>
<!--
 type constructor
 -->
-<o:function name="ex:QueenSolver">
-<o:do>
 <o:variable name="i" select="1"/>
-<o:while test="$i <= 8">
 <o:set lastQueen="ex:Queen($i, $lastQueen)"/>
 <o:do select="$lastQueen.findSolution()"/>
 <o:set i="$i+1"/>
 </o:while>
 </o:do>
 </o:function>
-<o:function name="paint">
-<o:do>
 <o:eval select="$lastQueen.paint()"/>
 </o:do>
 </o:function>
-<o:function name="advance">
-<o:do>
 <o:return select="$lastQueen.advance()"/>
 </o:do>
 </o:function>
 </o:type>
<!--
 end type definitions
 -->
<!--
 get the eight queens solver from the session
 -->
 <o:variable name="session" select="$servlet:req.getSession()"/>
 <o:variable name="solver" select="$session.getAttribute('eight-queens')"/>
-<o:choose>
-<o:when test="not($solver)">
<!--
 not there, create a new one
 -->
 <o:set solver="ex:QueenSolver()"/>
 </o:when>
-<o:otherwise>
<!--
 advance to next solution
 -->
-<o:if test="not($solver.advance())">
<!--
 no more solutions, create new queen solver
 -->
 <o:set solver="ex:QueenSolver()"/>
 </o:if>
 </o:otherwise>
 </o:choose>
-<solution>
 <o:eval select="$solver.paint()"/>
 </solution>
<!--
 save the solver for next time
 -->
 <o:do select="$session.setAttribute('eight-queens', $solver)"/>
 </o:program>