Maple's pretty printer understands how to display certain objects such as polynomials, plots, matrices, vectors, integrals, subscripts, etc. Users may now specify how their own functions are to be displayed as follows: To format a function foo the user may assign a Maple procedure to the name `print/foo`. The Maple procedure will be invoked during output of a Maple expression once for each different instance of foo in the output. The procedure can return any expression. Example:
> `print/complex` := proc(r,i) r+i*I end:
> complex(1,2);
1 + 2 I