seems to work...

app/Main.hs

@@ -1,8 +1,10 @@
 module Main where
 
+import System.IO
 import System.Directory
 import Options.Applicative
 import Data.List
+import Control.Exception
 
 data CgiState = CgiSuccess
 instance Show CgiState where
@@ -76,3 +78,9 @@ mkIndex True d f =
    in do
         line <- trim . words . head . lines <$> readFile path
         putStrLn $ "=> " ++ path ++ " " ++ line
+
+getFirstLine :: FilePath -> IO (Maybe String)
+getFirstLine f = (Just <$> readFile f) `catch` handler
+    where
+        handler :: IOException -> IO (Maybe String)
+        handler _ = return Nothing

flake.lock

@@ -5,11 +5,11 @@
         "systems": "systems"
       },
       "locked": {
-        "lastModified": 1689068808,
+        "lastModified": 1701680307,
-        "narHash": "sha256-6ixXo3wt24N/melDWjq70UuHQLxGV8jZvooRanIHXw0=",
+        "narHash": "sha256-kAuep2h5ajznlPMD9rnQyffWG8EM/C73lejGofXvdM8=",
         "owner": "numtide",
         "repo": "flake-utils",
-        "rev": "919d646de7be200f3bf08cb76ae1f09402b6f9b4",
+        "rev": "4022d587cbbfd70fe950c1e2083a02621806a725",
         "type": "github"
       },
       "original": {
@@ -20,11 +20,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1690753480,
+        "lastModified": 1705273882,
-        "narHash": "sha256-GQgPs8fCh/LsyQoYMUZgT2p7jFVWyHu9p+1Nl/dp8GY=",
+        "narHash": "sha256-68z5kaLaJ3fMWVwnknEKWypElq6Jzgtc9hddd14LhAo=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "9e06dd56947c1dc3dc837c3149bfe02c71a6edd7",
+        "rev": "5614bd58587f1337aca11d7b2bdfcca4ca44fccc",
         "type": "github"
       },
       "original": {

twin.cabal

@@ -67,7 +67,7 @@ executable twin
     -- other-extensions:
 
     -- Other library packages from which modules are imported.
-    build-depends:    base ^>=4.16.4.0, directory, optparse-applicative
+    build-depends:    base ^>=4.17.2.1, directory, optparse-applicative
 
     -- Directories containing source files.
     hs-source-dirs:   app