From a6247056a63d52b2253c4c88a0c9b988aaa4ebcd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Roman=20Smr=C5=BE?= <roman.smrz@seznam.cz>
Date: Sun, 13 Sep 2026 11:20:00 +0200
Subject: Replace IO-based fail with custom MonadFail instance for Eval

---
 src/Eval.hs | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

(limited to 'src/Eval.hs')

diff --git a/src/Eval.hs b/src/Eval.hs
index bd011cb..9d83758 100644
--- a/src/Eval.hs
+++ b/src/Eval.hs
@@ -48,10 +48,19 @@ textEvalError :: EvalError -> Text
 textEvalError (OtherEvalError text) = text
 
 
-type Eval a = ReaderT EvalInput (ExceptT EvalError IO) a
+newtype Eval a = Eval (ReaderT EvalInput (ExceptT EvalError IO) a)
+  deriving
+    ( Functor, Applicative, Monad
+    , MonadReader EvalInput
+    , MonadError EvalError
+    , MonadIO
+    )
+
+instance MonadFail Eval where
+    fail = throwError . OtherEvalError . T.pack
 
 runEval :: Eval a -> EvalInput -> IO (Either EvalError a)
-runEval action einput = runExceptT $ flip runReaderT einput action
+runEval (Eval action) einput = runExceptT $ flip runReaderT einput action
 
 
 eval :: forall ctx a. ctx -> Expr ctx a -> Eval a
-- 
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