On 08/03/12 16:19, Christopher Done wrote:
‘Ello.
Is there a generalization of this operator? It's all over the place,
it's basically
(!) :: (Monad m, Indexed collection index value) => index ->
container -> m value
We have `(!!)` on lists, `(!)` on maps, vectors, json objects, …
(doesn't seem there's one for bytestring)
(Though I seem to recall the monadic return value being frowned upon
but I don't recall why.)
Thoughts?
Ciao!
Ciao!
It doesn't exist as far as I know, but a "Map" typeclass can be easily
envisioned, e.g.:
{-# LANGUAGE MultiParamTypeClasses
, FunctionalDependencies
, FlexibleInstances
#-}
module MapClass (MapClass(..)) where
import Data.Map (Map)
import qualified Data.Map as Map
import Data.Hashable (Hashable)
import Data.HashMap.Lazy (HashMap)
import qualified Data.HashMap.Lazy as HashMap
import qualified Data.List as List
class MapClass m k v | m -> k, m -> v where
empty :: m
lookup :: k -> m -> Maybe v
insert :: k -> v -> m -> m
instance Ord k => MapClass [(k, v)] k v where
empty = []
lookup = List.lookup
insert k v = ((k, v) :)
instance Ord k => MapClass (Map k v) k v where
empty = Map.empty
lookup = Map.lookup
insert = Map.insert
instance (Hashable k, Eq k) => MapClass (HashMap k v) k v where
empty = HashMap.empty
lookup = HashMap.lookup
insert = HashMap.insert
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