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>>> import Data.List >>> permutations [1,2,3] [[1,2,3],[2,1,3],[3,2,1],[2,3,1],[3,1,2],[1,3,2]] comb :: Int -> [a] -> [[a]] comb 0 xs = [[]] comb _ [] = [] comb n (x:xs) = [x:y | y <- comb (n-1) xs] ++ comb n xs >>> import Control.Monad >>> replicateM 5 ["a", "b", "c"] [["a","a","a","a","a"],["a","a","a","a","b"],["a","a","a","a","c"],["a","a","a","b","a"],["a","a","a","b","b"],["a","a","a","b","c
「リストã®ãƒªã‚¹ãƒˆã«sequenceã‚’é©ç”¨ã™ã‚‹ã¨ç›´ç©ãŒå¾—られるã€ã®ã¯ãªãœã‹è€ƒãˆã‚‹ - エンジニアã®ã‚½ãƒ•ãƒˆã‚¦ã‚§ã‚¢çš„愛情
æ•™ãˆã¦ãれるã“ã¨ã‚’期待ã—ã¦æ€è€ƒåœæ¢ã—ã¦ã„るよã†ã§ã¯ãƒ€ãƒ¡ãƒ€ãƒ¡ãªã®ã§ã€ç†è§£ã§ãã‚‹ã¨ã“ã‚ã¾ã§è€ƒãˆã¦ã¿ã‚‹ã€‚ 基本ã«ç«‹ã¡è¿”ã‚‹ã¨ã€sequenceã®ã‚½ãƒ¼ã‚¹ã¯æ¬¡ã®ã‚ˆã†ã«ãªã£ã¦ã„ã‚‹ã®ãŒã“ã“ã‹ã‚‰ã‚ã‹ã‚‹ã€‚ sequence ms = foldr k (return []) ms where k m m' = do { x <- m; xs <- m'; return (x:xs) } ãã‚Œã»ã©é›£ã—ã„ã‚‚ã®ã§ã¯ãªã„。å•é¡Œã¯k m m'ã®éƒ¨åˆ†ã€‚ MaybeモナドやIOモナドãªã‚‰ã€ä½•ã¨ãªã予想ã¯ã¤ã。ã“れをリスト(Listモナド)ã«é©ç”¨ã™ã‚‹ã¨ã©ã†ãªã‚‹ã‹ãŒå•é¡Œã€‚ Prelude> let k m m' = do { x <- m; xs <- m'; return (x:xs) } Prelude> k "01" ["0", "1"] ["00","01","10","11"]ã“ã®çµæžœã‚’見れã°ã€sequenceã§ç›´ç©ãŒ
リストã®ãƒªã‚¹ãƒˆã«sequenceã‚’é©ç”¨ã™ã‚‹ã¨ç›´ç©ãŒå¾—られる - エンジニアã®ã‚½ãƒ•ãƒˆã‚¦ã‚§ã‚¢çš„愛情
ã©ã†æ›¸ã？orgã®ãŠé¡Œã‚ˆã‚Šã€‚ リストã®ãƒªã‚¹ãƒˆã«sequenceã‚’é©ç”¨ã™ã‚‹ã¨ç›´ç©ãŒå¾—られる。 $ ghci Prelude> sequence [[1,2,3], [4,5,6]] [[1,4],[1,5],[1,6],[2,4],[2,5],[2,6],[3,4],[3,5],[3,6]] Prelude> sequence ["abc", "def"] ["ad","ae","af","bd","be","bf","cd","ce","cf"] ã ã‹ã‚‰ã“ã†ã™ã‚‹ã¨ã€2進数(ã®æ–‡å—列)ã®ãƒªã‚¹ãƒˆãŒä½œã‚Œã‚‹ã€‚ Prelude> sequence $ replicate 4 "01" ["0000","0001","0010","0011","0100","0101","0110","0111","1000","1001","1010","1011","1100","1101","1110","11
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