Better handling of interrupts in REPL

README.md

@@ -10,7 +10,7 @@ tricu is the word for "tree" in Lojban: `(x1) is a tree of species/cultivar (x2)
 
 - Tree Calculus operator: `t`
 - Assignments: `x = t t`
-- Immutabile definitions
+- Immutable definitions
 - Lambda abstraction syntax: `id = (\a : a)`
 - List, Number, and String literals: `[(2) ("Hello")]` 
 - Function application: `not (not false)`
@@ -45,7 +45,7 @@ tricu > 12
 
 [Releases are available for Linux.](https://git.eversole.co/James/tricu/releases)
 
-Or you can easily build and/or run this project using [Nix](https://nixos.org/download/).
+Or you can easily build and run this project using [Nix](https://nixos.org/download/).
 
 - Quick Start (REPL): 
   - `nix run git+https://git.eversole.co/James/tricu`

src/Eval.hs

@@ -10,26 +10,26 @@ import qualified Data.Set as Set
 
 evalSingle :: Env -> TricuAST -> Env
 evalSingle env term
-  | SDef name [] body <- term =
-      if
-        | Map.member name env ->
-            errorWithoutStackTrace $
-              "Error: Identifier '" ++ name ++ "' is already defined."
-        | otherwise ->
-            let res = evalAST env body
-            in Map.insert "!result" res (Map.insert name res env)
-  | SApp func arg <- term =
-      let res = apply (evalAST env func) (evalAST env arg)
+  | SDef name [] body <- term
+  = case Map.lookup name env of
+      Just existingValue
+        | existingValue == evalAST env body -> env
+        | otherwise -> errorWithoutStackTrace $
+            "Unable to rebind immutable identifier: " ++ name
+      Nothing ->
+        let res = evalAST env body
+        in Map.insert "!result" res (Map.insert name res env)
+  | SApp func arg <- term 
+  = let res = apply (evalAST env func) (evalAST env arg)
       in Map.insert "!result" res env
-  | SVar name <- term =
-      case Map.lookup name env of
-        Just v  ->
-          Map.insert "!result" v env
+  | SVar name <- term 
+  = case Map.lookup name env of
+        Just v  -> Map.insert "!result" v env
         Nothing ->
           errorWithoutStackTrace $ "Variable `" ++ name ++ "` not defined\n\
           \This error should never occur here. Please report this as an issue."
-  | otherwise =
-      Map.insert "!result" (evalAST env term) env
+  | otherwise 
+  = Map.insert "!result" (evalAST env term) env
 
 evalTricu :: Env -> [TricuAST] -> Env
 evalTricu env x = go env (reorderDefs env x)

src/Main.hs

@@ -59,9 +59,8 @@ main = do
   case args of
     Repl -> do
       putStrLn "Welcome to the tricu REPL"
-      putStrLn "You can exit with `CTRL+D` or the `:_exit` command.`"
-      library <- liftIO $ evaluateFile "./lib/base.tri"
-      repl $ Map.delete "!result" library
+      putStrLn "You can exit with `CTRL+D` or the `!exit` command.`"
+      repl Map.empty
     Evaluate { file = filePaths, form = form } -> do
       result <- case filePaths of
         [] -> do
@@ -77,8 +76,7 @@ main = do
       value <- case filePaths of
         [] -> getContents
         (filePath:_) -> readFile filePath
-      library <- liftIO $ evaluateFile "./lib/base.tri"
-      putStrLn $ decodeResult $ result $ evalTricu library $ parseTricu value
+      putStrLn $ decodeResult $ result $ evalTricu Map.empty $ parseTricu value
 
 runTricu :: String -> T
 runTricu input =

src/REPL.hs

@@ -8,6 +8,7 @@ import Research
 
 import Control.Exception         (SomeException, catch)
 import Control.Monad.IO.Class    (liftIO)
+import Control.Monad.Catch (handle, MonadCatch)
 import Data.Char                 (isSpace)
 import Data.List                 (dropWhile, dropWhileEnd, intercalate)
 import System.Console.Haskeline
@@ -15,33 +16,37 @@ import System.Console.Haskeline
 import qualified Data.Map as Map
 
 repl :: Env -> IO ()
-repl env = runInputT defaultSettings (loop env)
+repl env = runInputT defaultSettings (withInterrupt (loop env))
   where
     loop :: Env -> InputT IO ()
-    loop env = do
+    loop env = handle (interruptHandler env) $ do
       minput <- getInputLine "tricu < "
-      if
-        | Nothing <- minput                     -> outputStrLn "Exiting tricu"
-        | Just s  <- minput, strip s == "!exit" -> outputStrLn "Exiting tricu"
-        | Just s  <- minput, strip s == ""      -> do
-          outputStrLn ""
-          loop env
-        | Just s  <- minput, strip s == "!import" -> do
-          path <- getInputLine "File path to load < "
-          if
-            | Nothing <- path -> do
-              outputStrLn "No input received; stopping import."
-              loop env
-            | Just p  <- path -> do
-              loadedEnv <- liftIO $ evaluateFileWithContext env (strip p) `catch` \e -> errorHandler env e
-              loop $ Map.delete "!result" (Map.union loadedEnv env)
-        | Just s <- minput -> do
-          if
-            | take 2 s == "--" -> loop env
-            | otherwise -> do
+      case minput of
+        Nothing -> outputStrLn "Exiting tricu"
+        Just s
+          | strip s == "!exit" -> outputStrLn "Exiting tricu"
+          | strip s == "" -> loop env
+          | strip s == "!import" -> do
+              path <- getInputLine "File path to load < "
+              case path of
+                Nothing -> do
+                  outputStrLn "No input received; stopping import."
+                  loop env
+                Just p -> do
+                  loadedEnv <- liftIO $ evaluateFileWithContext env 
+                    (strip p) `catch` \e -> errorHandler env e
+                  loop $ Map.delete "!result" (Map.union loadedEnv env)
+          | take 2 s == "--" -> loop env
+          | otherwise -> do
               newEnv <- liftIO $ processInput env s `catch` errorHandler env
               loop newEnv
 
+    interruptHandler :: Env -> Interrupt -> InputT IO ()
+    interruptHandler env _ = do
+      outputStrLn "Interrupted with CTRL+C\n\
+                  \You can use the !exit command or CTRL+D to exit"
+      loop env
+
     processInput :: Env -> String -> IO Env
     processInput env input = do
       let asts   = parseTricu input

tricu.cabal

@@ -26,6 +26,7 @@ executable tricu
     base >=4.7
     , cmdargs
     , containers
+    , exceptions
     , haskeline
     , megaparsec
     , mtl
@@ -52,6 +53,7 @@ test-suite tricu-tests
     base
     , cmdargs
     , containers
+    , exceptions
     , haskeline
     , megaparsec
     , mtl