I'd say that any polymorphic code that assumes that x==y implies x=y is
broken.
But apart from that, floating point numbers break all kinds of laws that we
might expect to hold. Even so, they are convenient to have instances of
various classes.
On Wed, Mar 12, 2008 at 7:31 PM, Adrian Hey
Remi Turk wrote:
I wouldn't bet on it either:
Prelude> 0.0 == -0.0 True Prelude> isNegativeZero 0.0 == isNegativeZero (-0.0) False
Although isNegativeZero might be considered a ``private, "internal" interface that exposes implementation details.''
Interesting example.
So is the correct conclusion from this that all (polymorphic) code that assumes (x == y) = True implies x=y is inherently broken, or is just this particular Eq instance that's broken?
Regards -- Adrian Hey
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