Re: [Haskell-cafe] Re: Why purely in haskell?

On 10 Jan 2008, at 7:55 AM, Achim Schneider wrote:

"Daniel Yokomizo" wrote:

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On Jan 10, 2008 3:36 PM, Achim Schneider wrote:

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jerzy.karczmarczuk@info.unicaen.fr wrote:

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Niko Korhonen writes:

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Although it could be argued that laziness is the cause of some very obscure bugs... <g> Niko

Example, PLEASE.

[1..] == [1..]

, for assumed operational semantics of ones own axiomatic semantics. Bugs are only a misunderstanding away.

It has nothing to do with laziness, but with using an algebraic function (==) with a codata structure (stream). If Haskell kept laziness but enforced separation of data and codata such code wouldn't compile. Lazy lists or streams never are a problem, but you can't (generically) fold codata.

Exactly. Denotationally it hasn't, but axiomatically it has. Because it looks like mathematical terms one can easily get lost in believing it reduces like mathematics, too.

What kind of mathematics? I don't know of any mathematics where algebraic simplifications are employed without proof of the underlying equations (in some denotational model). jcc