Hello Martin, Monday, December 8, 2008, 12:04:06 PM, you wrote:
Now it took me about a week to realise, that 'instance Ord Pat' causes ghc to loop.
naive Ord
instance Ord Exp
instance Ord Pat
i think you just don't learned this part of Haskell. empty instance declarations like these are possible but they doesn't mean automatic definition of some suitable compare. they just bring in some default definitions which may be mutual recursive, such as (==) and (/=) definitions in Eq class. this is intended to that your define either (==) or (/=), but compiler doesn't check this, so if you don't define anything, you will get endless loop if you want compiler to infer automatic instance definitions, the only way is to use GHC extension, smth like deriving instance Ord for Pat -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com