7 Jan
2008
7 Jan
'08
12:54 p.m.
On Mon, 2008-01-07 at 18:15 +0300, Miguel Mitrofanov wrote:
data Stack a = Stack { run :: [a] -> (a, [a]) }
[...skipped...]
But, I have simply no clue how to fix that. :-( Can anybody give my a hint?
Yes. It's simply impossible. The Stack data type can't be turned into a monad.
Indeed, the very first hint is that Stack isn't a functor because the type variable a occurs both positively and negatively.