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

On Fri, Dec 21, 2007 at 03:16:17PM -0800, David Benbennick wrote:

On Dec 21, 2007 2:30 PM, Don Stewart wrote:

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dbenbenn:

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Thanks for fixing this. But doesn't GHC have strictness analysis?

Sure does!

The problem here was an explicit recusive loop though, with just not enough for the strictness analyser to get going.

The explicit loop you're talking about is: enumDeltaInteger :: Integer -> Integer -> [Integer] enumDeltaInteger x d = x : enumDeltaInteger (x+d) d That code isn't very complicated, and I would hope to be able to write code like that in my own programs without having to worry about strictness. Given that the compiler even has an explicit signature, why can't it transform that code to enumDeltaInteger x d = let s = x + d in x : (seq s $ enumDeltaInteger s d) since it knows that (Integer+Integer) is strict? Of course, improving the strictness analysis is harder, but it pays off more, too.

Because they simply aren't the same. Try applying your functions to undefined undefined. Stefan