Don't require available library to run REPL or decoder

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

@@ -60,8 +60,7 @@ main = do
     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
+      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 =