On Friday 11 June 2010 07:47:03, Martin Drautzburg wrote:
On Friday, 11. June 2010 00:12:03 Daniel Fischer wrote:
Thanks Daniel.
Upgrade. We're at 6.12 now!
Did that. Everything is available now.
I am still having trouble with the test function. First it seems I need braces, so I can mix == and <*>. test :: Num a => (a -> a) -> (a -> a) -> (a -> a) -> [String] test f g h = do [f', g', h'] <- permutations [Named "f" f, Named "g" g, Named "h" h] guard $ namedPure 42 == (f' <*> g' <*> h' <*> namedPure 42) return $ show f' ++ " . " ++ show g' ++ " . " ++ show h'
But this leads to
Occurs check: cannot construct the infinite type: a = (a -> a) -> a1 -> t When generalising the type(s) for `test'
Ah, yes, (<*>) is left associative (infixl 4, hence you also need the parentheses since (==) is infix 4; same fixity and different associativities don't mix), here it must be associated to the right, namedPure 42 == (f' <*> (g' <*> (h' <*> namedPure 42))) :( If you'd want to use it a lot, define a right associative alias with higher fixity: infixr 5 <*< (<*<) = (<*>)
This error message is still the maximum penalty for me (along with "Corba marshall exception" in J2EE and "Missing right parenthesis" in Oracle SQL)
Then generally speaking, I have the feeling that this code does not allow "namifying" existing code either. In this respect it does not seem to do better than the "apply" method pattern discussed earlier in this thread.
You'd have to rewrite; either way.
The problem it solves is very simple and therefore using (<*>) and namedPure isn't much of a drawback. But if I had tons of code to namify I would still have to do significant changes to it, right?
Yes.