Fix GHC 9.8 warnings

lib/SlackBuilder/Info.hs

@@ -65,9 +65,11 @@ packageDownloads variableName = string (variableName <> "=\"")
     <* string "\"\n"
 
 hexDigit :: GenParser Word8
-hexDigit =
-    let digitPair = count 2 hexDigitChar
-     in fst . head . readHex . fmap (toEnum . fromIntegral) <$> digitPair
+hexDigit = count 2 hexDigitChar
+    >>= extractNumber . readHex . fmap (toEnum . fromIntegral)
+  where
+    extractNumber [(number, "")] = pure number
+    extractNumber _ = fail "Unable to convert a 2-digit hexadecimal number"
 
 packageChecksum :: GenParser ByteString
 packageChecksum = ByteString.pack <$> count 16 hexDigit

tests/SlackBuilder/InfoSpec.hs

@@ -65,8 +65,8 @@ spec = do
              in parseInfoFile' infoDownload1 `parseSatisfies` condition
 
         it "translates checksum characters into the binary format" $
-            let expected = "0102030405060708090a0b0c0d0e0f10"
-                condition = (== expected) . show . head . checksums
+            let expected = ["0102030405060708090a0b0c0d0e0f10"]
+                condition = (== expected) . fmap show . checksums
              in parseInfoFile' infoDownload1 `parseSatisfies` condition
 
         it "accepts an empty downloads list" $