[plt-scheme] Mixed fraction input

Right now when DrScheme gets "65/6" as output, it prints the mixed
fraction "10 5/6" out as a result (graphically, with a properly
vertical fraction).  It would be nice to be able to enter something
more like "10+5/6" to get this result, so that the input mirrors the
output and the programmer doesn't have to simplify their mixed
fractions.  I am aware of the "Insert Fraction..." menu option, but I
prefer to have as many text alternatives as possible.

Thanks if anyone can implement this.

--Carl