Re: foldl laziness support. Reply

On Mon, 2006-10-16 at 14:23 +0400, Serge D. Mechveliani wrote:

Concerning the laziness support problem,

I thank people for explanations about foldl and foldr.

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I wonder how to avoid these numerous cost pitfalls. Maybe, the complier could do more optimization?

Duncan Coutts writes

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There are important differences between foldl, foldl' and foldr. It is quite important to choose the right one. I don't think this can be done automatically.

In my experience, the choice is almost always between foldl' and foldr.

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I do not see foldl' in the standard library. Is it of the GHC lib extension? has it strictness annotation?

It's in the standard Data.List module. It's not in the Prelude. Duncan