在haskell中可能「調用數據結構中的函數」嗎？

Question

我有一些函數（charfreq，wordfreq，charcount，wordcount，parerror），我想用它在給定的字符串dataStructure.But我該怎麼做呢？我嘗試了這些和很多方式，但我得到了所有錯誤。提前感謝。

data StrStat = StrStat { charfreq :: [(Char , Int)] 
         , wordfreq :: [([ Char ] , Int)] 
         , charcount :: Int 
         , wordcount :: Int 
         , parerror::Maybe Int 
         } 


analyze :: [Char] -> StrStat 
analyze x = StrStat { charfreq = (charfreq x) {-this line gives error-} 
        , wordfreq = (wordfreq x) 
        , charcount = (charcount x) 
        , wordcount = (wordcount x) 
        , parerror = (parerror x) 
        } 

錯誤消息是：Syntax error in input (unexpected `=')

analyze :: [Char] -> StrStat 
analyze x = StrStat { "charfreq" = (charfreq x) 
        , "wordfreq" = (wordfreq x) 
        , "charcount" = (charcount x) 
        , "wordcount" = (wordcount x) 
        , "parerror" = (parerror x) 
        } 

當我試圖上一個，我在同一行得到了同樣的錯誤

Answer 1

我爲你的第一個版本的錯誤是

Couldn't match expected type `StrStat' with actual type `[Char]' 
In the first argument of `charfreq', namely `x' 
In the `charfreq' field of a record 
In the expression: 
    StrStat 
    {charfreq = (charfreq x), wordfreq = (wordfreq x), 
    charcount = (charcount x), wordcount = (wordcount x), 
    parerror = (parerror x)} 

這對我來說很有意義，因爲你正在申請你的獲得者（全部在你的中定義聲明，例如，charfreq :: StrStat -> [(Char , Int)]）正在對類型爲[Char]的數據調用，而不是在StrStat值上調用。

charfreq =等是基於關鍵字的參數，用於設置StrStat的各個字段，並且需要在其RHS上給出適當的值（例如[(Char, Int)]）。

我猜你正在試圖做的是建立一個StrStat值，你可以通過建立適當的值做：

import Control.Arrow 
import Data.List 

data StrStat = StrStat { charfreq :: [(Char , Int)] 
         , wordfreq :: [([ Char ] , Int)] 
         , charcount :: Int 
         , wordcount :: Int 
         , parerror::Maybe Int 
         } 

freq :: Ord a => [a] -> [(a, Int)] 
freq = map (head &&& length) . group . sort 

analyze :: [Char] -> StrStat 
analyze x = StrStat { charfreq = freq x 
        , wordfreq = freq $ words x 
        , charcount = length x 
        , wordcount = length $ words x 
        , parerror = Nothing 
        } 

〜