Imants

Thanks for the sanity check on the instances.

I am concerned about the use of the function immsucc' from the same paper, 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. 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 <imantc@gmail.com> 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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