[Haskell-beginners] Constructor classes and type classes.

[PATRICK BROWNE]

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/Relation.lhs>
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 at 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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