tricu

commit 5346e9d31a19c85ff0883268307a166441f4804b
parent 967892d64272badd188e1fea69f8240ec3cd3070
Author: James Eversole <james@eversole.co>
Date:   Mon, 27 Jan 2025 16:19:59 -0600

Gracefully ignore no-op redefs

Diffstat:
M
src/Eval.hs
 | 
32
++++++++++++++++----------------

1 file changed, 16 insertions(+), 16 deletions(-)
diff --git a/src/Eval.hs b/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)