Re: [Haskell-cafe] is proof by testing possible?

Neil Brown wrote:

Dan Piponi wrote:

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On Mon, Oct 12, 2009 at 10:42 AM, muad wrote:

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Is it possible to prove correctness of a functions by testing it? consider a function of signature

swap :: (a,b) -> (b,a)

We don't need to test it at all, it can only do one thing, swap its arguments. (Assuming it terminates.)

swap = undefined

Terminates and does not swap its arguments :-) What do free theorems say about this, exactly -- do they just implicitly exclude this possibility?

Normally, one presumes that "undefined" (id est, calling "error") is equivalent to looping, except that calling "error" is pragmatically speaking better: it is nicer to the caller of your function (they/you get to see a somewhat more descriptive error message instead of 100% CPU without any results). Regards, Jochem -- Jochem Berndsen | jochem@functor.nl | jochem@牛在田里.com