renderJValue (JString s) = show s

is not the same as

renderJValue (JString s) = s

You can easily see this with GHCi. A copy from my Windows session:

C:\>ghci

GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help

Loading package ghc-prim ... linking ... done.

Loading package integer ... linking ... done.

Loading package base ... linking ... done.

Prelude> let s = "Haskell"

Prelude> s

"Haskell"

Prelude> show s

"\"Haskell\""

Prelude> show (show s)

"\"\\\"Haskell\\\"\""

Prelude>

On Thu, Mar 26, 2009 at 4:41 PM, 7stud <bbxx789_05ss@yahoo.com> wrote:

In chapter 5, RWH defines a JValue data type like this:

SimpleJSON.hs:
--------------

module SimpleJSON
(
JValue(..)
) where

data JValue = JNumber Double
| JString String
| JArray [JValue]
| JObject [(String, JValue)]
| JBool Bool
| JNull
deriving (Eq, Ord, Show)

------------

Then RWH defines some functions like this:

PutJSON.hs:
----------
module PutJSON where

import SimpleJSON

renderJValue::JValue->String
renderJValue (JNumber f) = show f
renderJValue (JString s) = show s
renderJValue (JBool True) = "true"
renderJValue (JBool False) = "false"
renderJValue JNull = "null"
----------

My question is about the function:

renderJValue (JString s) = show s

A JString value contains a string, so why does the function use
show to convert s to a string? Why isn't that function defined
like this:

renderJValue (JString s) = s

Using that modified function seems to work:

Main.hs:
---------
module Main () where

import SimpleJSON
import PutJSON

main = let x = JString "hello"
in putStrLn (renderJValue x)

$ ghc -o simple Main.hs PutJSON.hs SimpleJSON.hs
/usr/libexec/gcc/i686-apple-darwin8/4.0.1/ld: warning -F: directory name
(/Users/me/Library/Frameworks) does not exist

$ simple
hello

Also can anyone tell me why I always get that warning?

Thanks

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