RE: Integer -> Int conversion

[Sigbjorn Finne (Intl Vendor)]

Andy Gill <[EMAIL PROTECTED]> writes: 
> 
> "Sigbjorn Finne (Intl Vendor)" wrote:
> > 
> > Hi,
> > 
> > there's difference in behaviour of how Integers are coerced Ints
> > between Hugs(98) and ghc.
> > 
> >    Prelude> (0x80000000 :: Int)
> > 
> >    Program error: {primIntegerToInt 2147483648}
> > 
> >    Prelude> (maxBound::Int) + 1
> >    -2147483648
> >    Prelude>
> > 
> > ghc's conversion of Integers is modulo maxInt, i.e.,
> > 
> >    (maxBound :: Int) + 1 == (0x80000000::Int)
> > 
> > is True.
> > 
> > That's consistent & handy, but whatever the behaviour used, it'd be
> > oh-so convenient if the two implementations agreed.
> 
> I think the current behavior of Hugs is reasonable.
> 

If you're saying that non-catchable, run-time exceptions are ok,
I'm not at all sure I agree!

> The question is what should 0x80000000 :: Integer
> become when its coerced into an int. 
> 
> GHC takes the lowest 32 bits.
>  Advantage: Equality above maxBound still "works" aka above.
>  Disadvantage: 0xffffffff + 1 == 0 !
> 
> Perhaps constant Int's larger than maxBound (or smaller
> than minBound) should be a compile time error? 
> 

Int arithmetic is modulo maxBound (at least that's what
ghc and Hugs implements), so making the Integer->Int conversion
fall into line with that, has some merit.

--sigbjorn