[Haskell-cafe] Re: Proof question -- (==) over Bool

[Daniel Fischer]

On Monday 24 May 2010 15:48:14, Jonas Almström Duregård wrote:
> >Consider that calling
> >
> >> id undefined
> >
> >requires evaluating undefined before you can call id.  The program will
> > "crash" before you ever call id.  Of >course, the identity function
> > "should" have produced a value that crashed in exactly the same way. 
> > But we >never got there.
>
> In which sense does id need to evaluate its argument?

It doesn't need to, and it doesn't. It just returns its argument untouched.

> If evaluating
> the statement "id undefined" in ghci, then the print function (and
> ultimately the show function) evaluates the undefined. I suppose that
> if the show function does not evaluate its argument then there will be
> no error, right?

Right:

Prelude Text.Show.Functions> id undefined :: (Bool -> Bool)
<function>

>
> /Jonas