Re: [Haskell-cafe] Why does this blow the stack?

dons:

dbenbenn:

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On 12/21/07, Stefan O'Rear wrote:

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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