Re: Static typing, polymorphism, inheritance

From: TLOlczyk (olczyk2002_at_yahoo.com)
Date: 11/01/03 

Date: Sat, 01 Nov 2003 03:02:38 -0600

On Fri, 31 Oct 2003 13:05:51 -0800, Costin Cozianu
<c_cozianu@hotmail.com> wrote:

>(* or even better, here's a polymorphic list : *)
>let myList= [ new person "Steve" 20 ; new employee "Costin" 20 1001]
>;;
There is a problem here.
myList;;
reveals that myList has type person list.

For the most part employee is treated OK in the list, but if you
add a method to either person or employee you will get errors
with myList.

The problem is not with typing but with the fact that [ ] generates
a homogeneous list. You would have to use an inhomogeneous list,
but I'm not that familiar with the library.

You can still see that there types are treated polymorphically via:

let g_print x s= x#print s;;

g_print x;;
g_print y;;