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