Dmitri O.Kondratiev wrote:
"Set" module here is built with list and uses among other things list comparison functions such as (==) and (<=).
Q1: Where "List" module is imported from?
GHC "Base" package contains "Data.List" module, not just "List" module.
List was the old name for it. Data.List is the new name.
Besides, "Data.List" does not have (<=) function.
Actually, lists are partly defined in the Prelude, with auxiliary functions in Data.List. In particular, <= for List is defined in the Prelude. Or rather, I should say, the Ord instance for lists is defined in the prelude (and only if the type inside the lists is itself an Ord instance). Look: Prelude> [1,2] <= [3,4] True (Lists of ints have the lexicographic ordering based on the standard ordering on integers) Prelude> [id] <= [id] <interactive>:1:5: No instance for (Ord (a -> a)) arising from use of `<=' at <interactive>:1:5-6 (Lists-of-functions aren't Ordered, because functions aren't Ordered) Jules