[Haskell-cafe] New to Haskell

[Henning Thielemann]

On Tue, 18 Dec 2007, Benja Fallenstein wrote:

> Hi Cristian,
>
> On Dec 18, 2007 10:53 AM, Cristian Baboi <cristi at ot.onrc.ro> wrote:
> > >> - the lambda expressions can be written (input) but cannot be printed
> > >> (output)
> >
> > > Yes, since two different lambda expressions can denote the same function.
> > I just want the sistem to be able to print one of these expressions !
> >
> > Its this too much to ask ?
> > I find it very strange that I can write a lambda expresion, but the system
> > cannot.
>
> It's a trade-off. Haskell has as a design goal that you can use
> equational reasoning everywhere -- that if you have two ways of
> writing the same function, you can substitute one for the other in any
> expression, without changing the result of that expression. For
> example, since you can prove
>
> sum = foldl (+) 0 = foldr (+) 0 = last . scanl (+) 0

Since this was discussed already here, I summed it up in:
  http://www.haskell.org/haskellwiki/Show_instance_for_functions