See my Double Argh message, but other than that, the only way is if you
redefine your Functor class to be a subclass of Get, which means you need
to define your own and cannot use the library one (unless something like
superclass is adopted...there's a recommendation out there for this
somewhere).
On Fri, 7 Mar 2003 07:47:09 -0800 (PST)
Hal Daume III [EMAIL PROTECTED] wrote:
That said, undecidable instances sound very scary, but they're
really not. You can google around for a conversation I had with SPJ
about this a while back, but something being an und instance is a
compile
It's in 7.3.5.3. I'm going to make it more prominent
S
| -Original Message-
| From: Hal Daume III [mailto:[EMAIL PROTECTED]
| Sent: 07 March 2003 15:08
| To: Nick Name
| Cc: Haskell Cafe
| Subject: RE: instance declaration troubles
|
| Double Argh! I just noticed that this isn't what
I want to declare the following:
class Get a where
ls :: a b - IO [b]
mk :: IO [b] - a b
instance (Get a) = Functor a where
fmap f x = mk (ls x = return . map f)
But to have ghc type everything, I have to turn on -fglasgow-exts
-fallow-undecidable-instances
