[Haskell-cafe] Defining show for a function type.

[Fritz Ruehr]

On Jul 10, 2006, at 8:44 AM, Johan Grönqvist wrote:

> "deriving Show" is impossible as Func is not instance of Show. Can I 
> make it instance of Show? I just want to define something like
>  ...
> and I am not interested in actually displaying any information about 
> the function, ...

Were you interested in "seeing" the function, you could do so, at least 
for finite, total functions (you can also enumerate them, compare them 
for equality, etc.). See my haskell-cafe message at 
<http://www.haskell.org/pipermail/haskell-cafe/2006-April/015197.html>.

By way of example, and quoting a sample interaction from that message:

> > not == not
> True
> > not == id
> False
> > id == (not . not)
> True
> > fromEnum not
> 1
> > not == toEnum 1
> True
> > not
> (\x -> case x of False -> True; True -> False)
> > not == (\x -> case x of False -> True; True -> False)
> True
> > id :: Bool -> Bool
> (\x -> case x of False -> False; True -> True)
> > const True :: Bool -> Bool
> (\x -> case x of False -> True; True -> True)

   --  Fritz
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