@Override
public String toString()
{
StringBuilder sb = new StringBuilder();
ProductRowType type = (ProductRowType)rowType();
int nFields = type.leftType().nFields() + type.rightType().nFields() - type.branchType().nFields();
sb.append("(");
for (int i = 0; i < nFields; ++i) {
if (i > 0) { sb.append(", "); }
ValueSources.toStringSimple(value(i), sb);