I was dealing with infix functions and have just discovered this Notation package It's really great!
For instance in time series, one could make the code more readable by using the following notation:
<< Notation`
Notation[ParsedBoxWrapper[
SubscriptBox["x_", "t_"]] \[DoubleLongLeftRightArrow] ParsedBoxWrapper[
RowBox[{"x_", "[[", "t_", "]]"}]]]
