prompt: added history file draft

bc.cabal

@@ -14,6 +14,6 @@ cabal-version:       >=1.10
 executable bc
   main-is:             Main.hs
   hs-source-dirs:      src/
-  build-depends:       base >=4.9 && <4.10, hashmap, parsec, unix
+  build-depends:       base >=4.9 && <4.10, directory, hashmap, parsec, unix
   hs-source-dirs:      src
   default-language:    Haskell2010

src/BC/Config.hs

@@ -5,3 +5,5 @@ versionStr = "0.1.0.0"
 promptStr = "> "
 
 returnStr = "=> "
+
+historyFile = ".bc_history"

src/BC/Prompt.hs

@@ -2,6 +2,8 @@ module BC.Prompt (startPrompt) where
 
 import Control.Monad (unless)
 import Data.Char
+import Data.List
+import System.Directory (doesFileExist, getHomeDirectory)
 import System.IO
 import System.Posix.Signals
 
@@ -15,6 +17,28 @@ import BC.Types
 data Prompt = PState Int [String]
 
 
+newPrompt :: IO Prompt
+newPrompt = do
+    home <- getHomeDirectory
+    let f = home ++ "/" ++ historyFile
+    exists <- doesFileExist f
+    if exists
+      then do
+        contents <- readFile f
+        return $ PState (-1) (split contents)
+      else return $ PState (-1) []
+  where split [] = []
+        split s = takeWhile (/= '\n') s : split (dropWhile (/= '\n') s)
+
+
+savePrompt :: Prompt -> IO ()
+savePrompt (PState _ strs) = do
+    home <- getHomeDirectory
+    f <- openFile (home ++ "/" ++ historyFile) WriteMode
+    hPrint f (intercalate "\n" strs)
+    hClose f
+
+
 printHeader :: IO ()
 printHeader = do
     putStrLn $ "bc (better calculator) version " ++ versionStr
@@ -124,12 +148,16 @@ readline state = read' "" 0
             | otherwise = n
 
 
-prompt :: State -> Prompt -> IO ()
+prompt :: State -> Prompt -> IO Prompt
 prompt state pstate@(PState _ history) = do
     input <- readline state pstate
     case input of
-      Nothing -> putStrLn "\nBye!"
-      Just "quit" -> putStrLn "\nBye!"
+      Nothing -> do
+        putStrLn "\nBye!"
+        return pstate
+      Just "quit" -> do
+        putStrLn "\nBye!"
+        return pstate
       Just str -> do
         putStrLn ""
         newstate <- output state str
@@ -149,4 +177,6 @@ startPrompt :: IO ()
 startPrompt = do
     printHeader
     installHandlers
-    prompt newState (PState (-1) [])
+    p <- newPrompt
+    state <- prompt newState p
+    savePrompt state