dons:
> dbenbenn:
> > On 12/21/07, Stefan O'Rear <[EMAIL PROTECTED]> wrote:
> > > Because they simply aren't the same.
> >
> > Good point; thanks. That means that Don's patch could theoretically
> > break some existing Haskell program:
> >
> > Prelude> length $ take 10 ([undefined ..] :: [Integer])
> > 10
>
> That's right. It makes Integer behave like the Int instance.
And we see again that strictness properties are very ill-defined,
here, the Enum types in base:
Prelude> length $ take 10 ([undefined ..] :: [Int])
*** Exception: Prelude.undefined
Prelude> length $ take 10 ([undefined ..] :: [()])
*** Exception: Prelude.undefined
Prelude> length $ take 10 ([undefined ..] :: [Ordering])
*** Exception: Prelude.undefined
Prelude> length $ take 10 ([undefined ..] :: [Bool])
*** Exception: Prelude.undefined
But,
Prelude> length $ take 10 ([undefined ..] :: [Float])
10
Prelude> length $ take 10 ([undefined ..] :: [Double])
10
And,
Prelude> length $ take 10 ([undefined ..] :: [Integer])
10
Now,
Prelude> length $ take 10 ([undefined ..] :: [Integer])
*** Exception: Prelude.undefined
So we see that Float and Double also have this problem,
Prelude> head (drop 10000000 [1 .. ]) :: Float
*** Exception: stack overflow
Prelude> head (drop 10000000 [1 .. ]) :: Double
*** Exception: stack overflow
People shouldn't be writing code that depends on this!
-- Don
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
