The pretty print arrow ==>

The "pretty print arrow" is similar to "=>" but will print complex lists and vectors out in a more readable form. E.g. using the variable rooms defined in Chapter 1, compare:

    rooms =>
    ** [[room1 10 12 8] [room2 6 11 8] [room3 15 11 8] [room4 10 12 9]
     [room5 21 11 9]]

    rooms ==>
    ** [[room1 10 12 8]
        [room2 6 11 8]
        [room3 15 11 8]
        [room4 10 12 9]
        [room5 21 11 9]]