Re: [Haskell-cafe] Newbie Q: GHCi: Where “List” module is imported from?
jules at jellybean.co.uk
Fri Feb 16 11:59:36 EST 2007
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
Prelude> [1,2] <= [3,4]
(Lists of ints have the lexicographic ordering based on the standard
ordering on integers)
Prelude> [id] <= [id]
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)
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