[Haskell-cafe] Wikipedia on first-class object

[Wolfgang Jeltsch]

Am Freitag, 28. Dezember 2007 07:49 schrieben Sie:
> On Thu, 27 Dec 2007 18:19:47 +0200, Wolfgang Jeltsch
> <g9ks157k at acme.softbase.org> 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.
>
> Thank you.
>
> I can only notice that y always has an even number of 1, which is not the
> case for x :-)

Both have an infinite number of 1.  Why do you say “always”?  It seems that 
you think of x and y as “variables” whose values change over time.  This is 
not the case.  They both have a single value for all time: the infinite list 
consisting only of 1.

Best wishes,
Wolfgang