Well, for JSON, I think the rendered string must be enclosed in double quotes, which is what the show instance for String does. So 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 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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Am Donnerstag 26 März 2009 16:41:47 schrieb 7stud:

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

The JSON values are rendered so that they can be parsed at the other end. The parser must have the string enclosed in quotation marks for that, also some characters need to be escaped. Consider having JString "true" JString "[true, null, false]" JString "This is a\nmultiline text.\b!"

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?

Does the directory exist? If it exists, is in in the linker path?

Thanks

On 2009 Mar 26, at 11:41, 7stud wrote:

$ 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

My guess is that the binary ghc was compiled to allow for use of private frameworks, so you get an unnecessary warning when you don't have any. Just create ~/Library/Frameworks if you want the warning to go away. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH