Thanks for the reply - since you mentioned that it should work I figured there must’ve been a mistake somewhere else. Looking closer I realised that when I copied & pasted the definition for (<) to the rest of the functions and the problem actually occurred at ... max a b = max (size a) (size b) min a b = min (size a) (size b) … which has return type of Double where it should be Cycle. Regards, Nicolaas On 11 Oct 2014, at 15:39, Brandon Allbery wrote:

On Sat, Oct 11, 2014 at 9:02 AM, Nicolaas du Preez wrote: data Cycle = Cycle { name :: String, size :: Double } deriving (Eq, Show)

instance Ord Cycle where (<) a b = (<) (size a) (size b) -- problem statement! …

How can I specify that, on the right-hand side of the problem statement, I refer to (<) :: Double -> Double -> Bool instead of (<) :: Cycle -> Cycle -> Bool?

That should be automatic, since it knows that size :: Cycle -> Double and therefore should use the Double instance. Can you provide a minimal full example and full error message?

-- brandon s allbery kf8nh sine nomine associates allbery.b@gmail.com ballbery@sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

Thanks for mentioning it; It saves a lot of copy & paste! On 12 Oct 2014, at 01:03, Nadir Sampaoli wrote:

To define an Ord instance you only need to implement compare because the other functions are derivable in terms of it. If you wany to explicitly implement max, a correct implementation could be: