Why Haskell have String Text and ByteString, what the hell is going on here?
There are 16 functions that convert among of them

String: What is that?
Why String is bad for you?
it implemented in single linked list
String is list of chars
"dog" = ['d', 'o', 'g']
when String is modified, Haskell allocates memory for it.
Also, since String is linked list, its memory locality is not good.

There are three type of string in Haskell:
String is slow one
Text is better performance
ByteString is for binary data

If you try to send serialize JSON, most likely you will use Aeson to encode and decode JSON, then you need to convert String to ByteString
and ByteString to String, and there are Strict and Lazy. You need conver
between Strict and Lazy. It is pain of the ass

Here are the functions that you need to use do conversion.
    import Data.ByteString.Lazy as BL
    import Data.ByteString as BS
    import Data.Text as TS
    import Data.Text.Lazy as TL
    import Data.ByteString.Lazy.UTF8 as BLU
    import Data.ByteString.UTF8 as BSU
    import Data.Text.Encoding as TSE
    import Data.Text.Lazy.Encoding as TLE
    -- String <-> ByteString
    BLU.toString   :: BL.ByteString -> String
    BLU.fromString :: String -> BL.ByteString
    BSU.toString   :: BS.ByteString -> String
    BSU.fromString :: String -> BS.ByteString
    -- String <-> Text
    TL.unpack :: TL.Text -> String
    TL.pack   :: String -> TL.Text
    TS.unpack :: TS.Text -> String
    TS.pack   :: String -> TS.Text
    -- ByteString <-> Text
    TLE.encodeUtf8 :: TL.Text -> BL.ByteString
    TLE.decodeUtf8 :: BL.ByteString -> TL.Text
    TSE.encodeUtf8 :: TS.Text -> BS.ByteString
    TSE.decodeUtf8 :: BS.ByteString -> TS.Text
    -- Lazy <-> Strict
    BL.fromStrict :: BS.ByteString -> BL.ByteString
    BL.toStrict   :: BL.ByteString -> BS.ByteString
    TL.fromStrict :: TS.Text -> TL.Text
    TL.toStrict   :: TL.Text -> TS.Text


Text: What is Text?
Why Text is bad or good for you?, it is slow for large String processing.
Text is array-based string representation.
Text is use something called fusion. 
When you convert Text and String, you will use pack and unpack, and there are Strict and Lazy of Text too.
So Lazy Text and Strict Text are different.


ByteString: What is ByteString?
Why ByteString is bad or good for you?
It is for binary data.

How do we convert them in each other?
pack
unpack
toString
toStrict
...