[Haskell-cafe] Re: instance Eq (a -> b)

[Maciej Piechotka]

On Wed, 2010-04-14 at 12:16 -0700, Ashley Yakeley wrote:
> On 2010-04-14 11:12, John Meacham wrote:
> > On Wed, Apr 14, 2010 at 02:07:52AM -0700, Ashley Yakeley wrote:
> >>> So the facts that
> >>> (1) f == g
> >>> (2) f undefined = 6
> >>> (3) g undefined = undefined
> >>> is not a problem?
> >>
> >> This is not a problem. f and g represent the same moral function,
> they
> >> are just implemented differently. f is smart enough to know that
> its
> >> argument doesn't matter, so it doesn't need to evaluate it. g waits
> >> forever trying to evaluate its function, not knowing it doesn't
> need it.
> >
> > Hence they are distinct functions,
> 
> They are distinct Haskell functions, but they represent the same
> moral 
> function.
> 

Are

f 0 = 1
f n = f (n - 1) + f (n - 2)

and

g 0 = 1
g n | n > 0 = g (n - 1) + g (n - 2)
    | n < 0 = g (n + 2) - g (n + 1)

The same (morally) function?

Are:

f x = 2*x

and

f x = undefined

The same function
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 836 bytes
Desc: This is a digitally signed message part
Url : http://www.haskell.org/pipermail/haskell-cafe/attachments/20100415/aceda99e/attachment.bin