CODEWITHSUNDEEP
jsonprinting
user008273
user008273

Reputation: 41

JSON printing format

I'm working with the type

data J = JObj[(String, J)]
     | JArr[J]
     | JStr String

When given the input :

JObj[("problem", "solving")]

I would like the output to be:

{"problem":"solving"}

But since JStr is a list, it keeps printing out {["problem", "solving"]} which is the way JStr was specified up above, but not what I want.

Here is what I have:

  show(JStr x) = show x
  show(JObj x) = "{" ++ show (foldl (x)) ++ "}"
  show(JArr x) = show x

I believe I can use map/ fold (is my implementation wrong?) on the list but I'm confused as to how to proceed further. I also thought of using intercalate & intersperse within Data.List to approach this. Thnks

Upvotes: 1

Views: 50

Answers (1)

J. Abrahamson
J. Abrahamson

Reputation: 74354

Consider the syntax at hand. For any pair (String, J) inside of the JObj list we'd like to eventually see (s, j) become "s": j

jpair :: (String, J) -> String
jpair (s, j) = show s ++ " : " ++ show j

Now, if we have a list [(String, J)] then we can produce a list of "s": j string fragments, but we need to combine them by interspersing commas instead of abusing the Haskell list syntax which would include the [ and ] brackets.

This functionality is available in Data.List.intersperse

intersperse :: a -> [a] -> [a]

or, even better, in Data.List.intercalate

intercalate :: [a] -> [[a]] -> [a]
intercalate med = concat . intersperse med

and we can use intercalate to get what we want

instance Show J where
  show(JStr x) = show x
  show(JObj x) = "{" ++ intercalate "," (map jpair x) ++ "}"
  show(JArr x) = show x

Upvotes: 2

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