can anyone help me figure out why this won't compile? I have a feeling the problem is:

.childSpanX(@parentIndex, @childIndex: 1) when (@childIndex < @parentIndex) // but i don't know why

`//added to bootstrap mixins.less

//variables
@gridColumns:             12;
@gridColumnWidth:      60px;
@gridGutterWidth:         20px;

.childSpanX(@parentIndex, @childIndex: 1) when (@childIndex < @parentIndex)
{
  (~"> .span@{childIndex}")
  {
    .childSpan(@parentIndex, @childIndex);
  }
  .childSpanX(@parentIndex, @childIndex + 1);  // recurse
}
// fallback
.childSpanX(0) {}

.parentSpanX(@parentIndex) when (@parentIndex > 0)
{
  (~".span@{parentIndex} > .row-fluid")
  {
    .childSpanX(@parentIndex); //call child fcn
  }
  .parentSpanX(@parentIndex - 1);  // recurse
}
// fallback to "break" the loop and avoid errors for no-match
.parentSpanX(0) {}


// output fcn
.childSpan (@parentColumns, @childColumns)
{
  @parentSpanPixelWidth: (@gridColumnWidth * @parentColumns) + (@gridGutterWidth * (@parentColumns - 1));
  @childSpanPixelWidth: (@gridColumnWidth * @childColumns) + (@gridGutterWidth * (@childColumns - 1));
  width: percentage(@childSpanPixelWidth / @parentSpanPixelWidth);
}

//after .row-fluid {}

.parentSpanX(@gridColumns);`

// trying to output:

.span11 > .row-fluid > .span1 { width: x%; } .span11 > .row-fluid > .span2 { width: xx%; } .span11 > .row-fluid > .span3 { width: xxx%; } etc
... .span10 > .row-fluid > .span1 { width: x%; } ... .span9 > .row-fluid > .span1 { width: x%; } etc