[Haskell-cafe] Re: Very freaky

On 2007-07-10, Dan Piponi wrote:

On 7/10/07, Andrew Coppin wrote:

...

But what does, say, "Maybe x -> x" say?

Maybe X is the same as "True or X", where True is the statement that is always true. Remember that the definition is

data Maybe X = Nothing | Just X

You can read | as 'or', 'Just' as nothing but a wrapper around an X and Nothing as an axiom.

So Maybe X -> X says that "True or X" implies X. That's a valid proposition.

It is? Doesn't look like it. Unless you just mean "grammatical" by valid, rather than "true". The standard function of this type is "fromJust" fromJust (Just x) = x It's incomplete, of course. fromMaybe :: a -> Maybe a -> a is complete, and (X => (True or X) => X) certainly is a true proposition. -- Aaron Denney -><-