/** Creates an expr, handling some special cases. */
public static Expr create(AbstractPattern pattern) {
if (pattern instanceof NodeTypePattern
&& pattern.getParent() instanceof FromSelf
&& pattern.toString().equals(".")) return new ObjectExpr(SELF, ".");
else if (pattern instanceof FromContext
&& ((FromContext) pattern).getCount() == 0
&& pattern.getParent() == null) return new ObjectExpr(SELF, ".");
else if (pattern instanceof NodePattern
&& pattern.getParent() instanceof FromAttributes
&& pattern.getParent().getParent() instanceof FromContext
&& ((FromContext) pattern.getParent().getParent()).getCount() == 0)
return new ObjectExpr(ATTRIBUTE, ((NodePattern) pattern).getNodeName());
else return new NodeSetExpr(pattern);
}
