On Tue, 10 Jul 2012, Sönke Hahn wrote:
Hi!
I've discovered a strange bug that violates simple equational reasoning. Basically, something similar to this:
let a = f x in a == f x
While this code as it stands doesn't quite illustrate the referential transparency error, since == isn't guarenteed to return True on the same floating point value (see NaN), with a small tweek we can turn into an example that does illustrate the lack of referential transparency: (let a = f x in a == f x) == (let a = f x in a == a) or also perhaps (let a = f x in a == f x) == (f x == f x) If either of these return False than it is an error of referential transparency since equality on equivalent Bool expressions is always supposed to return True or diverge. -- Russell O'Connor http://r6.ca/ ``All talk about `theft,''' the general counsel of the American Graphophone Company wrote, ``is the merest claptrap, for there exists no property in ideas musical, literary or artistic, except as defined by statute.''