[Haskell-cafe] How to check object's identity?
jan.h.xie at gmail.com
Sat Jan 3 10:51:12 EST 2009
Thanks guys :-)
* Nicolas Pouillard <nicolas.pouillard at gmail.com> [2009-01-03 16:39:59 +0100]:
> Excerpts from Xie Hanjian's message of Sat Jan 03 16:28:30 +0100 2009:
> > Hi,
> > I tried this in ghci:
> > >Prelude> 1:2: == 1:2:
> > True
> > Does this mean (:) return the same object on same input, or
> > (==) is not for identity checking? If the later is true, how
> > can I check two object is the *same* object?
> Here (==) is the structural equality. There is generally no exposed function
> to check for identity of values. This would expose too much of the memory
> model and the compilation process to give a specification to such a function.
> Nicolas Pouillard
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