Re: More on type sizes

[kenner at vlsi1 dot ultra dot nyu dot edu (Richard Kenner)]

    >     We had to go through various contortions dealing with (say) a
    >     TYPE_MAX_VALUE of -1.  
    > 
    > I don't see why.

    For example if the index type is defined as a sub-type of an
    unsigned integer type.  In that case, -1 one is not in the
    index type, and in fact TYPE_MAX_VALUE is undefined.  

It's interesting that Chill allows that.  In Ada (and I though Chill
and Ada had some common heritage), the bounds of *any* array, whether
empty or not, much be values in the index type.

In Ada, if I have

	type Index is 20 .. 30;
	type Arr is array (Index range <>) of Character;

I can have members of type Arr that have bounds 30..29, 20..10, or 10..5
(all of which are empty), but *not* 31..30, since 31 is not a member of its
index type.

Can you say more about the typing rules of Chill in this area?

But my feeling is that if indeed a bound of Chill array can be outside the
bounds of its index type, then the index type actually in the tree needs to
be a different type, one that can contain all the values that are permitted
to be in the type.  That seems, to me, the cleanest approach, by far.