Imants Thanks for the sanity check on the instances. I am concerned about the use of the function immsucc' from the same paper http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.36.9395, which is defined in instances the Time class (but omitted from the class). The function immsucc' is first used without arguments, which to me implies that it 'might' a function passed to the higher-order closure function. It is then used as just an ordinary function with arguments. I have found a version of closure based on Craft of Function Programming. https://github.com/buntine/Haskell--Craft-of-FP/blob/master/AbsTypes/Relatio... which does not require a function as an argument. So basically my question is: does the usage of immsucc' make sense in the code below?, do the types match up? Regards, Pat data TimeFacts t = Bef (t, t, TimeFacts t) | New class SetClass t => Time l t where new :: (t, t) -> l t bef :: (t, t, l t) -> l t succ , pred :: (t, l t) -> Set t immsucc , immpred :: (t, l t) -> Set t before, after :: (t, t, l t) -> Bool immedbefore, immedafter :: (t, t, l t) -> Bool immedafter (a, b, t) = immedbefore (b, a, t) after (a, b, t) = before (b, a, t) before (a, b, t) = memberInSet (b, succ (a, t)) succ (a, tl) = closure ([a], immsucc' , tl) pred (a, tl) = closure ([a], immpred' , tl) immsucc (a, tl) = immsucc' ([a], [], tl) immpred (a, tl) = immpred' ([a], [], tl) instance (SetClass t) => Time TimeFacts t where immsucc’ (a, s, New ) = s immsucc’ (a, s, Bef (e, f, tt)) = if memberInSet (e,a) then immsucc’ (a, insertInSet (f,s), tt) else immsucc’ (a, s,tt) On 3 November 2016 at 18:05, Imants Cekusins wrote:

this builds. not sure if the instances are as intended

{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances #-} module SetClass where

data TimeFacts t = Bef (t, t, TimeFacts t) | New

class SetClass t where class SetClass t => Time l t where class Time l t => TimeE l t where class Time l t => TimeTO l t where

instance SetClass (TimeFacts t) where -- OK instance (SetClass t) => Time (TimeFacts t) t where instance (SetClass t) => TimeE (TimeFacts t) t where instance (SetClass t) => TimeTO (TimeFacts t) t where

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