[Haskell-cafe] generalized newtype deriving allows the definition
of otherwise undefinable functions
g9ks157k at acme.softbase.org
Tue Mar 9 10:04:17 EST 2010
Am Dienstag, 9. März 2010 15:54:16 schrieb Jan-Willem Maessen:
> On Mar 9, 2010, at 5:53 AM, Max Cantor wrote:
> > Isn't this just an extension of the notion that multi-parameter
> > typeclasses without functional dependencies or type families are
> > dangerous and allow for type-naughtiness?
> I wondered the same thing, but came up with an analogous problematic case
> that *only* uses generalized newtype deriving:
Originally, I had a more restricted example in mind which is similar to yours.
However, I wanted to generalize the problem and therefore introduced the
general Iso class which made MultiParamTypeClasses and FlexibleInstances
necessary. The actual problem is related neither to MultiParamTypeClasses nor
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