adeMacBook-Pro:haskell_dev apple$ ghci
GHCi, version : http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Prelude> putStrLn "Hello World"
Hello World
Prelude> 

-- file: ch05/SimpleJSON.hs
data JValue = JString String
| JNumber Double
| JBool Bool
| JNull
| JObject [(String, JValue)]
| JArray [JValue]
deriving (Eq, Ord, Show)

-- file: ch05/SimpleJSON.hs
getString :: JValue -> Maybe String
getString (JString s) = Just s
getString _ = Nothing

-- file: ch05/SimpleJSON.hs
getInt (JNumber n) = Just (truncate n)
getInt _ = Nothing

getDouble (JNumber n) = Just n
getDouble _ = Nothing

getBool (JBool b) = Just b
getBool _ = Nothing

getObject (JObject o) = Just o
getObject _ = Nothing

getArray (JArray a) = Just a
getArray _ = Nothing

isNull v = v == JNull

main = print (JObject [("foo", JNumber 1), ("bar", JBool False)])

adeMacBook-Pro:haskell_dev apple$ ghci

GHCi, version 7.8.3: http://www.haskell.org/ghc/  :? for help

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

Loading package integer-gmp ... linking ... done.

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

Prelude> :load SimpleJSON.hs

[1 of 1] Compiling Main             ( SimpleJSON.hs, interpreted )

Ok, modules loaded: Main.

*Main> getString (JString "hello")

Just "hello"

*Main>  getString (JNumber 3)

Nothing

*Main> getString (JString "hello")

Just "hello"

*Main>

adeMacBook-Pro:haskell_dev apple$ ls

Assign.hs       InteractWith.hi SimpleJSON.hs   WC.o            myDrop.hs

BookStore.hs    InteractWith.hs WC              add.hs          quux.txt

HelloWorld.hs   InteractWith.o  WC.hi           hello-in.txt    upperCase.hs

InteractWith    Maybe           WC.hs           hello-out.txt

adeMacBook-Pro:haskell_dev apple$ ghc SimpleJSON.hs

[1 of 1] Compiling Main             ( SimpleJSON.hs, SimpleJSON.o )

Linking SimpleJSON ...

adeMacBook-Pro:haskell_dev apple$ ls

Assign.hs       InteractWith.hs SimpleJSON.hs   WC.o            quux.txt

BookStore.hs    InteractWith.o  SimpleJSON.o    add.hs          upperCase.hs

HelloWorld.hs   Maybe           WC              hello-in.txt

InteractWith    SimpleJSON      WC.hi           hello-out.txt

InteractWith.hi SimpleJSON.hi   WC.hs           myDrop.hs

adeMacBook-Pro:haskell_dev apple$ ls

Assign.hs       InteractWith.hs SimpleJSON.hs   WC.o            quux.txt

BookStore.hs    InteractWith.o  SimpleJSON.o    add.hs          upperCase.hs

HelloWorld.hs   Maybe           WC              hello-in.txt

InteractWith    SimpleJSON      WC.hi           hello-out.txt

InteractWith.hi SimpleJSON.hi   WC.hs           myDrop.hs

adeMacBook-Pro:haskell_dev apple$ ./SimpleJSON

JObject [("foo",JNumber 1.0),("bar",JBool False)]

adeMacBook-Pro:haskell_dev apple$ runghc SimpleJSON.hs

JObject [("foo",JNumber 1.0),("bar",JBool False)]