Revision: 50505
Updated Code
at August 25, 2011 02:20 by rtperson
Updated Code
{-# LANGUAGE Arrows #-} import Control.Arrow import Data.List list = "abcdefghijklmnop" -- the trivial version removeAt n xs = take (n-1) xs ++ (drop n) xs -- now new and improved! with Arrows for ultra-obfuscation! removeAt' :: (Arrow cat) => Int -> cat [a] [a] removeAt' n = arr(\ xs -> (xs,xs)) >>> arr (take (n-1)) *** arr (drop n) >>> arr (uncurry (++)) >>> returnA {- the arrowed function is easier to understand in its sugary form NOTE: the head and tail of the arrows are lambda values, so they can't be used inside the arrow's machinery. Also, to use this notation, you'll need the LANGUAGE Arrows pragma -} removeAt'' :: Int -> [a] -> [a] removeAt'' n = proc things -> do (begin, end) <- (\xs -> (xs, xs)) -< things begin' <- take (n-1) -< begin end' <- drop n -< end newlist <- uncurry (++) -< (begin', end') returnA -< newlist -- This is equivalent, and shows how proc notation can -- simplify things removeAt''' :: Int -> [a] -> [a] removeAt''' n = proc things -> do begin <- take (n-1) -< things end <- drop n -< things returnA -< begin ++ end main = do putStrLn list putStrLn $ removeAt 3 list putStrLn $ removeAt' 5 list putStrLn $ removeAt'' 9 list
Revision: 50504
Updated Code
at August 25, 2011 02:14 by rtperson
Updated Code
{-# LANGUAGE Arrows #-} import Control.Arrow import Data.List list = "abcdefghijklmnop" -- the trivial version removeAt n xs = take (n-1) xs ++ (drop n) xs -- now new and improved! with Arrows for ultra-obfuscation! removeAt' :: (Arrow cat) => Int -> cat [a] [a] removeAt' n = arr(\ xs -> (xs,xs)) >>> arr (take (n-1)) *** arr (drop n) >>> arr (uncurry (++)) >>> returnA {- the arrowed function is easier to understand in its sugary form NOTE: the head and tail of the arrows are lambda values, so they can't be used inside the arrow's machinery. Also, to use this notation, you'll need the LANGUAGE Arrows pragma -} removeAt'' :: Int -> [a] -> [a] removeAt'' n = proc things -> do (begin, end) <- (\xs -> (xs, xs)) -< things begin' <- take (n-1) -< begin end' <- drop n -< end newlist <- uncurry (++) -< (begin', end') returnA -< newlist main = do putStrLn list putStrLn $ removeAt 3 list putStrLn $ removeAt' 5 list putStrLn $ removeAt'' 9 list
Revision: 50503
Updated Code
at August 25, 2011 02:11 by rtperson
Updated Code
{-# LANGUAGE Arrows #-} import Control.Arrow import Data.List -- the trivial version removeAt n xs = take (n-1) xs ++ (drop n) xs -- now new and improved! with Arrows for ultra-obfuscation! removeAt' :: (Arrow cat) => Int -> cat [a] [a] removeAt' n = arr(\ xs -> (xs,xs)) >>> arr (take (n-1)) *** arr (drop n) >>> arr (uncurry (++)) >>> returnA {- the arrowed function is easier to understand in its sugary form NOTE: the head and tail of the arrows are lambda values, so they can't be used inside the arrow's machinery. Also, to use this notation, you'll need the LANGUAGE Arrows pragma -} removeAt'' :: Int -> [a] -> [a] removeAt'' n = proc things -> do (begin, end) <- (\xs -> (xs, xs)) -< things begin' <- take (n-1) -< begin end' <- drop n -< end newlist <- uncurry (++) -< (begin', end') returnA -< newlist
Revision: 50502
Updated Code
at August 25, 2011 01:59 by rtperson
Updated Code
import Control.Arrow import Data.List -- the trivial version removeAt n xs = take (n-1) xs ++ (drop n) xs -- now new and improved! with Arrows for ultra-obfuscation! removeAt' :: (Arrow cat) => Int -> cat [a] [a] removeAt' n = arr(\ xs -> (xs,xs)) >>> arr (take (n-1)) *** arr (drop n) >>> arr (uncurry (++)) >>> returnA
Revision: 50501
Initial Code
Initial URL
Initial Description
Initial Title
Initial Tags
Initial Language
at August 25, 2011 01:54 by rtperson
Initial Code
-- the trivial version removeAt n xs = take (n-1) xs ++ (drop n) xs -- now new and improved! with Arrows for ultra-obfuscation! removeAt' :: (Arrow cat) => Int -> cat [a] [a] removeAt' n = arr(\ xs -> (xs,xs)) >>> arr (take (n-1)) *** arr (drop n) >>> arr (uncurry (++)) >>> returnA
Initial URL
http://haskell.org/haskellwiki/99_questions/11_to_20
Initial Description
problem 20, (*) Remove the K'th element from a list *Main> removeAt 1 "abcd" "acd" Trivial using a pure function. A bit more challenging if you use this problem to work up your Arrow-fu.
Initial Title
Haskell 99 Problems - Number 20, Arrowed!
Initial Tags
Initial Language
Haskell