CODEWITHSUNDEEP
functionhaskelldata-structures
oiyio
oiyio

Reputation: 5925

is "calling functions in data structure" possible in haskell?

i have some functions(charfreq,wordfreq,charcount,wordcount,parerror) and i want to use it in dataStructure with the given string.But how can i do it? I'm trying in these and many way ,but i got all error .Thanks in advance .

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) 
                    }

error message is : 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) 
                    }

when i tried previous one , i got the same error at the same line

Upvotes: 1

Views: 233

Answers (1)

rampion
rampion

Reputation: 89043

The error I get for your first version is

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)}

Which makes sense to me, as you're applying your getters (all defined in your data StrStat declaration, for example, charfreq :: StrStat -> [( Char , Int )]) are being called on data of type [Char], rather than on a StrStat value.

The charfreq = and such are keyword-based arguments for setting the various fields of the StrStat, and need to be given the appropriate value (e.g. [(Char, Int)]) on their RHS.

What I'm guessing you're trying to do is to construct a StrStat value, which you could do by constructing appropriate values:

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
                    }

~

Upvotes: 5

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