public static QilTuple GetTuple(QilTuple context) {
Debug.Assert(context != null);
if (context.For.Type == QilNodeType.Let) {
Debug.Assert(context.Where.Type == QilNodeType.True);
Debug.Assert(context.Return.Type == QilNodeType.OldTuple);
return (QilTuple) context.Return;
}
return context;
}
public static QilTuple GetTuple(QilTuple context)
{
Debug.Assert(context != null);
if (context.For.Type == QilNodeType.Let)
{
Debug.Assert(context.Where.Type == QilNodeType.True);
Debug.Assert(context.Return.Type == QilNodeType.OldTuple);
return((QilTuple)context.Return);
}
return(context);
}
public static QilNode GetCurrentPosition(QilFactory f, QilTuple context) {
Debug.Assert(context != null);
if (context.Where.Type != QilNodeType.True) {
Debug.Assert(context.For.Type == QilNodeType.For);
// convert context (1) --> (2)
QilIterator for2 = f.For(context.For.Binding);
QilNode cnd2 = new Replacer(f).Replace(/*inExpr:*/context.Where, /*from:*/context.For, /*to:*/for2);
context.For.Binding = f.OldTuple(for2, cnd2, for2);
context.Where = f.True();
}
return f.Convert(f.PositionOf((QilIterator)XPathContext.GetCurrentNode(context)), f.TypeFactory.Double());
}
public static QilNode GetCurrentPosition(QilFactory f, QilTuple context)
{
Debug.Assert(context != null);
if (context.Where.Type != QilNodeType.True)
{
Debug.Assert(context.For.Type == QilNodeType.For);
// convert context (1) --> (2)
QilIterator for2 = f.For(context.For.Binding);
QilNode cnd2 = new Replacer(f).Replace(/*inExpr:*/ context.Where, /*from:*/ context.For, /*to:*/ for2);
context.For.Binding = f.OldTuple(for2, cnd2, for2);
context.Where = f.True();
}
return(f.Convert(f.PositionOf((QilIterator)XPathContext.GetCurrentNode(context)), f.TypeFactory.Double()));
}
public static QilNode GetLastPosition(QilFactory f, QilTuple context)
{
return(f.Convert(f.Length(context.Clone(f)), f.TypeFactory.Double()));
}
// Context is the most fundamental concept of XPath
// In docs it is -- "current node-set" and "current node in this node-set"
// on practice in this implementation we have "current node" (C), "position of current node in current node-set" (P)
// and "size of the current node-set" (S)
// All XPath expressions consume context, "step" expressions change it
// In this XPath implementation we passing context as Tuple.
// In most cases this Tuple has For iterator bind to some expression.
// (1): Tuple1( For1(bind1), cond{For1}, For1 )
// To take (C) from such context XPath uses its For1 iterator.
//
// (P) is little bit more complex. It should be PositionOf(For1) but this will be correct only if
// cond{For1} == True
// To enforce this (1) can be rewritten as
// (2): Tuple1( For1(Tuple2( For2(bind1), cond{For2}, For2 ), True, For1 )
// Note: cond{For2} is result of replacing For1 to For2 in cond{For1}
//
// (S) most complex case. We want to cash with Let variable node-set we are iterating:
// (3): Tuple1( Let(Tuple2( For2(bind1), cond{For2}, For2) ), True, Tuple3( For1(Let), True, For1 ) )
// (S) = SetLength(Let); (P) = PositionOf(For1)
//
// So 3: is most generic representation of XPath context while (1) & (2) is its simplified form.
// We always create context node as (1) and convert it to (2) & (3) on demand.
// XPath function position() force (1) -> (2) transformation if condition != true
// XPath function last() force (1) -> (3) or (2) -> (3) transformation if node-set wasn't cashed yet.
//
// Consider expression "foo[bar + position() + last()]"
// "foo" ==> Tuple1(For1(Content(XmlContext)), Name(For1)=='foo', For1))
// "bar" ==> Tuple2(For2(Content(For1 )), Name(For2)=='bar', For2))
//
// "position()" ==> PositionOf(For1)
// After "foo" was rewritten as:
// "for" ==> Tuple1(For1(Tuple3(For3(Content(XmlContext)), Name(For3)=='foo', For3)), True, For1)
// Note1: all external references to "foo" expression are still valid because we didn't change Tuple1
// Note2: "bar" is still valid because it refers to For1.
// Note3: "Name(For1)=='foo'" was rewritten as "Name(For3)=='foo'"
// "last()" ==> SetLength(Let)
// "for" ==> Tuple1(Let(Tuple3(For3(Content(XmlContext)), Name(For3)=='foo', For3)), True, Tuple4(For1(Let), True, For1))
// Note2: "bar" and "position" are still valid because they refer to For1.
// Issue:
// What restriction we should put on return value of context tuple.
// In XSLT when we fixing up call-templates return value shouldn't be touched
// In simple XPath a/b[2] return value is pure iterator and can be left as it is
// In more complex XPath (a/b)[2] resturn value is Tuple and should be isolated with context.
// this can be done as grouping as well.
// XSLT complies for-each and apply-templates in form (2) so converting to (3) shouldn't be a problem
// -- It look like solution is group (a/b) with For(DocOrderDistinct(...)) and we are set.
// Methods that deal with XPath context. Xslt.QilGenerator calls these method as well:
public static QilNode GetCurrentNode(QilTuple context)
{
Debug.Assert(context != null);
Debug.Assert(GetTuple(context).For.Type == QilNodeType.For);
return(GetTuple(context).For);
}
public static QilNode GetLastPosition(QilFactory f, QilTuple context) {
return f.Convert(f.Length(context.Clone(f)), f.TypeFactory.Double());
}
// Context is the most fundamental concept of XPath
// In docs it is -- "current node-set" and "current node in this node-set"
// on practice in this implementation we have "current node" (C), "position of current node in current node-set" (P)
// and "size of the current node-set" (S)
// All XPath expressions consume context, "step" expressions change it
// In this XPath implementation we passing context as Tuple.
// In most cases this Tuple has For iterator bind to some expression.
// (1): Tuple1( For1(bind1), cond{For1}, For1 )
// To take (C) from such context XPath uses its For1 iterator.
//
// (P) is little bit more complex. It should be PositionOf(For1) but this will be correct only if
// cond{For1} == True
// To enforce this (1) can be rewritten as
// (2): Tuple1( For1(Tuple2( For2(bind1), cond{For2}, For2 ), True, For1 )
// Note: cond{For2} is result of replacing For1 to For2 in cond{For1}
//
// (S) most complex case. We want to cash with Let variable node-set we are iterating:
// (3): Tuple1( Let(Tuple2( For2(bind1), cond{For2}, For2) ), True, Tuple3( For1(Let), True, For1 ) )
// (S) = SetLength(Let); (P) = PositionOf(For1)
//
// So 3: is most generic representation of XPath context while (1) & (2) is its simplified form.
// We always create context node as (1) and convert it to (2) & (3) on demand.
// XPath function position() force (1) -> (2) transformation if condition != true
// XPath function last() force (1) -> (3) or (2) -> (3) transformation if node-set wasn't cashed yet.
//
// Consider expression "foo[bar + position() + last()]"
// "foo" ==> Tuple1(For1(Content(XmlContext)), Name(For1)=='foo', For1))
// "bar" ==> Tuple2(For2(Content(For1 )), Name(For2)=='bar', For2))
//
// "position()" ==> PositionOf(For1)
// After "foo" was rewritten as:
// "for" ==> Tuple1(For1(Tuple3(For3(Content(XmlContext)), Name(For3)=='foo', For3)), True, For1)
// Note1: all external references to "foo" expression are still valid because we didn't change Tuple1
// Note2: "bar" is still valid because it refers to For1.
// Note3: "Name(For1)=='foo'" was rewritten as "Name(For3)=='foo'"
// "last()" ==> SetLength(Let)
// "for" ==> Tuple1(Let(Tuple3(For3(Content(XmlContext)), Name(For3)=='foo', For3)), True, Tuple4(For1(Let), True, For1))
// Note2: "bar" and "position" are still valid because they refer to For1.
// Issue:
// What restriction we should put on return value of context tuple.
// In XSLT when we fixing up call-templates return value shouldn't be touched
// In simple XPath a/b[2] return value is pure iterator and can be left as it is
// In more complex XPath (a/b)[2] resturn value is Tuple and should be isolated with context.
// this can be done as grouping as well.
// XSLT complies for-each and apply-templates in form (2) so converting to (3) shouldn't be a problem
// -- It look like solution is group (a/b) with For(DocOrderDistinct(...)) and we are set.
// Methods that deal with XPath context. Xslt.QilGenerator calls these method as well:
public static QilNode GetCurrentNode(QilTuple context) {
Debug.Assert(context != null);
Debug.Assert(GetTuple(context).For.Type == QilNodeType.For);
return GetTuple(context).For;
}
