Marc Weber wrote:
structure My_Ord : MY_ORD = struct
class strict_less a = a -> a -> bool
fun lt [a] (f: strict_less a) (x:a) (y:a) = f x y
(* causing Can't resolve type class instance
Class constraint: Basis.eq a
*)
fun le [a] (f: strict_less a) (x:a) (y:a) = f x y || x = y
end
The le implementation does not know which eq implementation to use ?
Perhaps it would be useful for you to review the concept of type classes
in Haskell. They are very similar in Ur.
In your code above, nowhere have you declared that type [a] belongs to
class [eq], so of course you are not allowed to use [=] on [a] values.
Two solutions that come to mind:
1) Add an [eq a] argument to [le].
2) Extend the definition of [strict_less a] to contain an [eq a], too.
(Though this seems to create some dissonance with the words "strict less"!)
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