[Haskell-cafe] Re: Why purely in haskell?

Cristian Baboi cristi at ot.onrc.ro
Fri Jan 11 05:50:53 EST 2008

On Fri, 11 Jan 2008 09:11:52 +0200, Lennart Augustsson  
<lennart at augustsson.net> wrote:

> Some people seem to think that == is an equality predicate.
> This is a big source of confusion for them; until they realize that == is
> just another function returning Bool they will make claims like  
> [1..]==[1..]
> having an unnatural result.
> The == function is only vaguely related to the equality predicate in  
> that it
> is meant to be a computable approximation of semantic equality (but since
> it's overloaded it can be anything, of course).

Imagine one can manage to define a function which stops when applied on  
any value of type T1, but not when applied on some values of type T2  
including bottom. Because bottom is a member of any type and referential  
transparency  must not be broken, such a function cannot be defined.

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