Ross, Thanks very much. I was going to use coal :: Vector a -> [a] coal = coal_ (\() -> []) (\x -> [x]) but I prefer your definitions. Dominic. ----- Original Message ----- From: "Ross Paterson" <ross@soi.city.ac.uk> To: "Dominic Steinitz" <dominic.steinitz@blueyonder.co.uk> Cc: <haskell@haskell.org> Sent: Saturday, September 20, 2003 5:19 PM Subject: Re: Polymorphic Recursion / Rank-2 Confusion
On Sat, Sep 20, 2003 at 12:01:32PM +0100, Dominic Steinitz wrote:
Can anyone tell me why the following doesn't work (and what I have to do to fix it)? I thought by specifying the type of coalw as rank-2 would allow it to be used both at a and (a,b).
Change the signature to
coal_ :: (v -> [a]) -> (w -> [a]) -> Vector_ v w -> [a]
Then you can define
type Vector = Vector_ ()
coal :: Vector a -> [a] coal = coal_ (const []) (:[])