我想检查列表中的任何元素是否与其他列表Haskell的任何元素相匹配 [英] I want to check if any element of a list matches any element of other list Haskell

问题描述

  type Domino = [（Int，Int）] 
 Hand = Domino 
 type Board = Hand 
 type End = Board 
 
 
 dominoes :: Domino 
 dominoes = [（x，y）| x < -  [0..6]，y < -  [x..6]] 
 
 amount_to_take = 7 
 
 hand :: Domino  - > Domino 
 hand x = take amount_to_take x 
  

我想检查Domino的任何元素是否匹配与任何元素的结束。如果它返回true，否则返回false

  goesP :: Domino  - >结束 - > Bool 
 goesP（h：t）（h1：t1）
 | h == h1 = True 
 | t == t1 = True 
 |否则False 
  

解决方案

  goesP :: Domino  - >结束 - > Bool 
 goesP（h：t）（h1：t1）
 | h == h1 =真 - 看起来合法。 
 | t == t1 = True  - 呃...这将检查整个SUBLIST是否相等。 
 |否则为假 - 在这里应该是等号。 
  

另外，如果其中一个列表为空，会发生什么？你只能匹配非空的情况。

如果你想手动（即不使用现有库函数），你可能需要一些东西像这样：

  goesP :: Domino  - >结束 - > Bool 
 goesP [] _ = False  - 跑出Dominos检查。 
 goesP（d：ds）e = hunt d e || goP ds e 
其中
 hunt d [] =假 - 结束检查。 
 hunt d（e：es）=（d == e）||搜寻
  

如果您想使用库函数执行此操作：

  goesP :: Domino  - >结束 - > Bool 
 goesP de = any（`elem` d）e 
  

Hoogle 找出原因。

module Dominoes where

type Domino = [(Int, Int)]
type Hand = Domino
type Board = Hand
type End = Board


dominoes :: Domino
dominoes = [(x, y)| x <- [0..6], y <- [x..6]]

amount_to_take = 7

hand :: Domino -> Domino
hand x  = take amount_to_take x

I want to check if any element of Domino matches with any element of End. Returning true if it does and false if it doesn't

goesP :: Domino -> End -> Bool 
goesP (h:t) (h1:t1) 
  |   h == h1 = True
  |   t == t1 = True
  |  otherwise False

解决方案

goesP :: Domino -> End -> Bool
goesP (h:t) (h1:t1)
  | h == h1 = True   -- Seems legit.
  | t == t1 = True   -- Er... this checks if the ENTIRE SUBLIST is equal.
  | otherwise False  -- Should be an equals sign here.

Also, what happens if either of the lists is empty? You're only matching the non-empty case.

If you want to do this "by hand" (i.e., without using existing library functions), you probably want something like this:

goesP :: Domino -> End -> Bool
goesP []     _ = False -- Ran out of Dominos to check.
goesP (d:ds) e = hunt d e || goesP ds e
  where
    hunt d []     = False -- Run out of Ends to check.
    hunt d (e:es) = (d == e) || hunt d es

If you want to do this with library functions:

goesP :: Domino -> End -> Bool
goesP d e = any (`elem` d) e

Have a go at hitting Hoogle to find out why that works.

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