[M3devel] INTEGER

[hendrik at topoi.pooq.com]

On Thu, Apr 22, 2010 at 02:36:17PM -0400, Tony Hosking wrote:
> Let me see.
> 
> The green book definition says the base type of a subrange of INTEGER literals is INTEGER.
> You say that the base type of a subrange of LONGINT literals is LONGINT.
> But you say that LONGINT is not a defined type.  So, what is the type 
> of a LONGINT literal?

(a) 3849587394875493920398438483929293484L could very well be of type 
3849587394875493920398438483929293484L..3849587394875493920398438483929293484L
which is a one-element subtype of LONGINT.

LONGINY is a type.  It's just one that's not available directly to the 
programmer.  It would not need to have a defined size, if the language 
allowed LONGINT values to occur *only* where an upper bound on 
their size is known, such as by being elements of a subrange.

-- hendrik

> 
> [I think I misunderstood you previously. I had interpreted that you meant LONGINT subranges to have base type INTEGER.]
> 
> On 22 Apr 2010, at 08:38, hendrik at topoi.pooq.com wrote:
> 
> > On Thu, Apr 22, 2010 at 11:57:16AM -0400, Tony Hosking wrote:
> >> But this is bizarre.  What type does an element of a subrange of 
> >> LONGINT have if not LONGINT?
> > 
> > It has LONGINT as a type.
> > 
> >> If the subrange has a base type of INTEGER then we need a mapping 
> >> between the elements of the subrange and the base INTEGER values.
> > 
> > Yes.  And INTEGER is different from the notion mathematicians have of 
> > integers in that there is a limit on the size of integers.  It's a 
> > machine or implementation-dependent limit, and it's imposed for 
> > efficiency reasons, but it's a specific limit just the same.
> > This limit is precisely what we're up against.
> > 
> >> But then, values of the LONGINT subrange don't have the same 
> >> representation as their INTEGER counterpart.
> > 
> > Of course not.  If they did have the same representation, there would be 
> > in-range for INTEGERs, and there would be no need to have LONGINT at 
> > all.
> > 
> > LONGINT is there precisely for the integers that *don't* fit in INTEGER.
> > 
> >> 
> >> All very odd.
> > 
> > But dictated by the intended use -- that of having integral ranges
> > whose bounds are dictated by the problem, not the hardware.
> > 
> > -- hendrik
>