Haskell: steps 0-3

1 files changed, 93 insertions, 0 deletions

diff --git a/haskell/step2_eval.hs b/haskell/step2_eval.hs
new file mode 100644
index 0000000..0a95fcc
--- /dev/null
+++ b/haskell/step2_eval.hs
@@ -0,0 +1,93 @@
+import System.IO (hGetLine, hFlush, hIsEOF, stdin, stdout)
+import Control.Monad (when, mapM)
+import Control.Monad.Error (throwError)
+import qualified Data.Map as Map
+import qualified Data.Traversable as DT
+
+import Types
+import Reader (read_str)
+import Printer (_pr_str)
+
+-- read
+mal_read :: String -> IO MalVal
+mal_read str = read_str str
+
+-- eval
+eval_ast :: MalVal -> (Map.Map String MalVal) -> IO MalVal
+eval_ast (MalSymbol sym) env = do
+    case Map.lookup sym env of
+         Nothing -> error $ "'" ++ sym ++ "' not found"
+         Just v  -> return v
+eval_ast ast@(MalList lst) env = do
+    new_lst <- mapM (\x -> (eval x env)) lst
+    return $ MalList new_lst
+eval_ast ast@(MalVector lst) env = do
+    new_lst <- mapM (\x -> (eval x env)) lst
+    return $ MalVector new_lst
+eval_ast ast@(MalHashMap lst) env = do
+    new_hm <- DT.mapM (\x -> (eval x env)) lst
+    return $ MalHashMap new_hm
+eval_ast ast env = return ast
+
+apply_ast :: MalVal -> (Map.Map String MalVal) -> IO MalVal
+apply_ast ast@(MalList _) env = do
+    el <- eval_ast ast env
+    case el of
+         (MalList (MalFunc (FuncT f) : rest)) ->
+            return $ f $ MalList rest
+         el ->
+            error $ "invalid apply: " ++ (show el)
+
+eval :: MalVal -> (Map.Map String MalVal) -> IO MalVal
+eval ast env = do
+    case ast of
+         (MalList lst) -> apply_ast ast env
+         _             -> eval_ast ast env
+
+
+-- print
+mal_print :: MalVal -> String
+mal_print exp = show exp
+
+-- repl
+add args = case args of
+    (MalList [MalNumber a, MalNumber b]) -> MalNumber $ a + b
+    _ -> error $ "illegal arguments to +"
+sub args = case args of
+    (MalList [MalNumber a, MalNumber b]) -> MalNumber $ a - b
+    _ -> error $ "illegal arguments to -"
+mult args = case args of
+    (MalList [MalNumber a, MalNumber b]) -> MalNumber $ a * b
+    _ -> error $ "illegal arguments to *"
+divd args = case args of
+    (MalList [MalNumber a, MalNumber b]) -> MalNumber $ a `div` b
+    _ -> error $ "illegal arguments to /"
+
+repl_env :: Map.Map String MalVal
+repl_env = Map.fromList [("+", _malfunc add),
+                         ("-", _malfunc sub),
+                         ("*", _malfunc mult),
+                         ("/", _malfunc divd)]
+
+rep :: String -> IO String
+rep line = do
+    ast <- mal_read line
+    exp <- eval ast repl_env
+    return $ mal_print exp
+
+repl_loop :: IO ()
+repl_loop = do
+    putStr "user> "
+    hFlush stdout
+    ineof <- hIsEOF stdin
+    when (not ineof) $ do
+        line <- hGetLine stdin
+        if null line
+            then repl_loop
+            else do
+                out <- catchAny (rep line) $ \e -> do
+                    return $ "Error: " ++ (show e)
+                putStrLn out
+                repl_loop
+
+main = repl_loop