On 27 Dec 2007, at 10:44 AM, Achim Schneider wrote:
Wolfgang Jeltsch <[EMAIL PROTECTED]> wrote:
Am Donnerstag, 27. Dezember 2007 16:34 schrieb Cristian Baboi:
I'll have to trust you, because I cannot test it.
let x=(1:x); y=(1:y) in x==y .
I also cannot test this:
let x=(1:x); y=1:1:y in x==y
In these examples, x and y denote the same value but the result of x
== y is _|_ (undefined) in both cases. So (==) is not really
equality in Haskell but a kind of weak equality: If x doesn’t equal
y, x == y is False, but if x equals y, x == y might be True or
undefined.
[1..] == [1..] certainly isn't undefined, it always evaluates to True,
If something happens, it does eventually happen.
More importantly, we can prove that [1..] == [1..] = _|_, since
[1..] == [1..]
= LUB (n >= 1) [1..n] ++ _|_ == [1..n] ++ _|_
= LUB (n >= 1) _|_
= _|_
jcc
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