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{-# LANGUAGE ParallelListComp,
TransformListComp,
RecordWildCards #-}
module Test10312 where
-- From
-- https://ocharles.org.uk/blog/guest-posts/2014-12-07-list-comprehensions.html
import GHC.Exts
import qualified Data.Map as M
import Data.Ord (comparing)
import Data.List (sortBy)
-- Let’s look at a simple, normal list comprehension to start:
regularListComp :: [Int]
regularListComp = [ x + y * z
| x <- [0..10]
, y <- [10..20]
, z <- [20..30]
]
parallelListComp :: [Int]
parallelListComp = [ x + y * z
| x <- [0..10]
| y <- [10..20]
| z <- [20..30]
]
-- fibs :: [Int]
-- fibs = 0 : 1 : zipWith (+) fibs (tail fibs)
fibs :: [Int]
fibs = 0 : 1 : [ x + y
| x <- fibs
| y <- tail fibs
]
fiblikes :: [Int]
fiblikes = 0 : 1 : [ x + y + z
| x <- fibs
| y <- tail fibs
| z <- tail (tail fibs)
]
-- TransformListComp
data Character = Character
{ firstName :: String
, lastName :: String
, birthYear :: Int
} deriving (Show, Eq)
friends :: [Character]
friends = [ Character "Phoebe" "Buffay" 1963
, Character "Chandler" "Bing" 1969
, Character "Rachel" "Green" 1969
, Character "Joey" "Tribbiani" 1967
, Character "Monica" "Geller" 1964
, Character "Ross" "Geller" 1966
]
oldest :: Int -> [Character] -> [String]
oldest k tbl = [ firstName ++ " " ++ lastName
| Character{..} <- tbl
, then sortWith by birthYear
, then take k
]
groupByLargest :: Ord b => (a -> b) -> [a] -> [[a]]
groupByLargest f = sortBy (comparing (negate . length)) . groupWith f
bestBirthYears :: [Character] -> [(Int, [String])]
bestBirthYears tbl = [ (the birthYear, firstName)
| Character{..} <- tbl
, then group by birthYear using groupByLargest
]
uniq_fs = [ (n, the p, the d') | (n, Fixity p d) <- fs
, let d' = ppDir d
, then group by Down (p,d') using groupWith ]
|
