On 2009 Mar 16, at 8:48, Yusaku Hashimoto wrote:
On 2009/03/16, at 10:04, wren ng thornton wrote:Moreover, let's have two pure implementations, f and g, of the same mathematical function. Even if f and g are close enough to correctly give the same output for inputs with _|_ in them, we may be able to observe the fact that they arrive at those answers differently by passing in our x. Given that such observations are possible, it is no longer safe to exchange f and g for one another, despite the fact that they are pure and give the same output for all (meaningful) inputs.Hm, Does it means that in optimization, a compiler may replace implementation of a pure function that have different order of evaluation, so order of actions would be different in some environments?
"order of actions" is meaningless in pure functions, so yes. And that's why unsafeInterleaveIO is unsafe: your pure function can have side effects which are observable, so there is an order of actions to worry about.
-- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH
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