Add fenv starter

fenv.hs

@@ -0,0 +1,53 @@
+import System.Environment
+import System.Directory
+import System.IO
+import Data.List
+
+type EnvKey = String
+type EnvValue = String
+
+data EnvFile =
+    End
+    | Entry EnvKey EnvValue EnvFile
+    deriving (Show,Eq,Read)
+
+main = do
+    let f = (Entry "foo" "bar" End)
+    putStrLn (show f)
+
+setEntry :: EnvFile -> EnvKey -> EnvValue -> EnvFile
+setEntry env key value = let env'=(removeEntry env key) in
+                            (Entry key value env')
+
+removeEntry :: EnvFile -> EnvKey -> EnvFile
+removeEntry End _ = End
+removeEntry (Entry entryKey entryValue rest) key = if entryKey==key
+                                                    then rest
+                                                    else (Entry entryKey entryValue (removeEntry rest key))
+
+getEntry :: EnvFile -> EnvKey -> Maybe EnvValue
+getEntry End _ = Nothing
+getEntry (Entry entryKey entryValue rest) key = if entryKey==key
+                                                    then return entryValue
+                                                    else (getEntry rest key)
+
+replaceEnvFile :: EnvFile -> IO ()
+replaceEnvFile env = do
+    path <- getEnvFilePath
+    (tempName, tempHandle) <- openTempFile "/tmp" ".fenv"
+    hPutStr tempHandle (show env)
+    hClose tempHandle
+    removeFile path
+    renameFile tempName path
+
+getEnvFile :: IO EnvFile
+getEnvFile = do
+    path <- getEnvFilePath
+    contents <- readFile path
+    return $ read contents
+
+getEnvFilePath :: IO FilePath
+getEnvFilePath = do
+    home <- getHomeDirectory
+    return (home ++ "/.fenv")
+