[Haskell-cafe] Newbie Question on type constructors

[Ben Rudiak-Gould]

Finn Wilcox wrote:

 >On Mon, 1 Nov 2004, Ben Rudiak-Gould wrote:
 >
 >>In particular, one cannot write an invert :: (a->b) -> Maybe
 >>(b->a) which never returns a wrong answer, except for invert = const
 >>Nothing
 >
 >How about:
 >
 >invert = undefined
 >
 >This never returns an answer at all, so it can't return a wrong one!

Sorry, I should have been clearer: my Nothing return was intended to 
mean "I don't know an answer", not "there is no answer". So my const 
Nothing is like your undefined, a function which never returns an answer 
(and thus never returns a wrong one).

-- Ben