[Haskell-cafe] Re: Laws and partial values
Miguel Mitrofanov
miguelimo38 at yandex.ru
Sat Jan 24 17:42:05 EST 2009
On 25 Jan 2009, at 00:11, Thomas Davie wrote:
> I'm coming at this from the point of view that bottom would contain
> all the information we could possibly know about a value while
> still being the least value in the set.
Note that we can't possibly know what information can we possibly know
about a value being given it's type.
For example, you can prove that the only "reasonable" value of type
(forall a. a -> a) is (id); so, from you POV, (_|_) :: forall a. a ->
a is equal to (id). This means, that
((_|_) :: forall a. a -> a) 1 = 1
instead of (_|_). But there is no way for a compiler to deduce all the
equalities of this kind.
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