Question

1.如何计算嵌套在元组中的数量

联合时出现2.got错误，即使嵌套数量相同，如何联合这个元组列表？

错误：

<interactive>:13:1:
    No instance for (Eq Expr) arising from a use of `union'
    Possible fix: add an instance declaration for (Eq Expr)
    In the expression: union b1 b2
    In an equation for `it': it = union b1 b2

haskell代码：

countnest :: (Int,Int) -> Int
countnest ((a1,a2), (b1,b2)) = max (max ((countnest (fst (a1,a2)))+1) ((countnest (snd (a1,a2)))+1)) (max ((countnest (fst (b1,b2)))+1) ((countnest (snd (b1,b2)))+1))
countnest (a1, (b1,b2)) = max 0 (max ((countnest (fst (b1,b2)))+1) ((countnest (snd (b1,b2)))+1))
countnest ((a1,a2), b1) = max (max ((countnest (fst (a1,a2)))+1) ((countnest (snd (a1,a2)))+1)) 0
countnest (a1, a2) = 1
countnest a1 = 1

rotate :: Int -> [a] -> [a]
rotate _ [] = []
rotate n xs = zipWith const (drop n (cycle xs)) xs

rev2 :: [a] -> [a]
rev2 (x:[]) = [x]
rev2 (x:xs) = rev xs ++ [x]

flatten1 :: [[a]] -> [a]
flatten1 xss = foldr (++) [] xss

getUniqueOrder :: (Ord a) => [[a]] -> [[a]]
getUniqueOrder xs = nub ( map sort xs)

getUnique :: (Ord a) => [[a]] -> [[a]]
getUnique xs = nub (xs)

data Expr = A | B | C | D | S | M2 | M1 | MM1 deriving (Show)
let cartProd xs ys = [(x,y) | x <- xs, y <- ys]
let m1 = cartProd [A,S] [B,M2]
let m2 = (cartProd (cartProd (cartProd [A,S] [B,M2]) [C,M1]) [D])  
let m3 = m2 ++ [(((S,MM1),MM1),MM1)]

let a1 = m3
let b1 = [rotate y a1 | y <- [0..(length a1 -1)]]
let a2 = rev a1
let b2 = [rotate y a2 | y <- [0..(length a2 -1)]]
union b1 b2

当编译countnest得到错误时，经过多次尝试，仍然不能找到哪里错了，已经匹配模式

*Main> :l oo.hs
[1 of 1] Compiling Main             ( oo.hs, interpreted )

oo.hs:140:12:
    Couldn't match expected type `Int'
                with actual type `((Int, Int), (Int, Int))'
    In the pattern: (a1, a2)
    In the pattern: ((a1, a2), (b1, b2))
    In an equation for `countnest':
        countnest ((a1, a2), (b1, b2))
          = max
              (max
                 ((countnest (fst (a1, a2))) + 1) ((countnest (snd (a1, a2))) + 1))
              (max
                 ((countnest (fst (b1, b2))) + 1) ((countnest (snd (b1, b2))) + 1))

oo.hs:140:21:
    Couldn't match expected type `Int'
                with actual type `((Int, Int), (Int, Int))'
    In the pattern: (b1, b2)
    In the pattern: ((a1, a2), (b1, b2))
    In an equation for `countnest':
        countnest ((a1, a2), (b1, b2))
          = max
              (max
                 ((countnest (fst (a1, a2))) + 1) ((countnest (snd (a1, a2))) + 1))
              (max
                 ((countnest (fst (b1, b2))) + 1) ((countnest (snd (b1, b2))) + 1))

Answer 1

countnest :: (Int,Int) -> Int
countnest ((a1,a2), (b1,b2)) = ...

此处的函数定义与声明不一致。但这不仅仅是一个错误：你所呼唤的东西＆＃34; tuple＆＃34;实际上是一棵树，所以你可能需要这样的代码：

data NestType = ConsLeaf Int | ConsPair NestType NestType

countnest :: NestType -> Int
countnest (ConsLeaf _) = 1
countnest (ConsPair x y) = max (countnest x) (countnest y) +1

如何计算元组中嵌套的数量以及如何结合这个元组列表

1 个答案: