Dictionaries and sets

A number of useful data structures are defined in the containers package.

Maps

Like a Python dictionary, this has unique (and orderable) keys, and arbitrary values. These must be of a single type.

repl example

import qualified Data.Map as M

> hasRedHat = M.fromList [("John", True), ("Sally", False), ("Jane", True)]
> hasRedHat
fromList [("Jane",True),("John",True),("Sally",False)]
> :t hasRedHat
hasRedHat :: M.Map String Bool
> :t M.fromList
M.fromList :: Ord k => [(k, a)] -> M.Map k a

-- look up
> M.lookup "John" hasRedHat 
Just True
> M.lookup "Jim" hasRedHat
Nothing

Sets

repl example

> import qualified Data.Set as S
> S.fromList [1,3,2,1,5,4,3]
fromList [1,2,3,4,5]

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