在哈斯克尔"calling functions in data structure"可能吗？

Question

我有一些函数（charfreq、wordfreq、charcount、wordcount、parerror），我想在给定字符串的dataStructure中使用它。但是我该怎么做呢？我尝试了很多方法，但都错了。提前谢谢。

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) 
                    }

错误消息为：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) 
                    }

当我尝试上一个时，我在的同一行得到了相同的错误

Answer 1

我得到的第一个版本的错误是

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)}

这对我来说很有意义，因为在应用getter时（所有getter都在data StrStat声明中定义，例如charfreq :: StrStat -> [( Char , Int )]）是对类型为[Char]的数据调用的，而不是对StrStat值调用的。

charfreq =等是用于设置StrStat的各个字段的基于关键字的自变量，并且需要在它们的RHS上被赋予适当的值（例如[(Char, Int)]）。

我猜你想做的是构造一个StrStat值，你可以通过构造适当的值来实现：

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
                    }

~