[Haskell-beginners] Pattern matching over functions

[Ertugrul Söylemez]

Graham Gill <math.simplex at gmail.com> wrote:

> > > But then we would lose referential transparency.
> >
> > As I understand, this would be against lazy evaluation since it
> > would request to evaluate expressions in lambda, but I don't see how
> > this relates to referential transparency.  Can you elaborate this a
> > little bit?
>
> I second the question.

Referential transparency /requires/ that

    id x = x

even if 'x' is a function, and this can, as Brent already noted,
arbitrarily complicated.  If pattern matching could tell f from id f,
then referential transparency is violated.  The only possible way to
tell f from id f is very unsafe and needs IO, hence not usable in
pattern matching.


Greets,
Ertugrul

-- 
nightmare = unsafePerformIO (getWrongWife >>= sex)
http://ertes.de/
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