Hello Haskellers, I hope I chose proper mailing list, if not I apologize. And thanks for reading this! I run into a problem with HStringTemplate ( http://hackage.haskell.org/package/HStringTemplate) that I have never seen before. Code, similar to {-# LANGUAGE OverloadedStrings, DeriveDataTypeable, NoImplicitPrelude #-} module Main where import Data.Data import qualified Data.Text as T import qualified Text.StringTemplate as Template renderTextTemplate :: (Template.ToSElem a) => T.Text -> a -> IO T.Text renderTextTemplate name input = do templatesGroup <- Template.directoryGroup "templates" case Template.getStringTemplate (T.unpack name) templatesGroup of Nothing -> return $ "Internal Error: template '" `mappend` name `mappend` "' can not be rendered" Just template -> return $ Template.render (Template.setAttribute "it" input (template:: Template.StringTemplate T.Text)) data Foo = Foo {value:: T.Text} deriving (Data, Typeable) main :: IO () main = do content <- renderTextTemplate "test" $ Foo {value = "oh hi there!"} putStrLn content with a simple template like this: Just a test $it.value$! started to cause complaints from GHC (7.8.2 and 7.8.4 on Linux x86_64): No instance for (Template.ToSElem Foo) Problem is - it didn't do that before. What even more confusing, older project[0] uses same approach, compiles (same machine, same compiler) and works just fine! I've exhausted all means to fix the problem that I could think off: - Adding 'instance Template.ToSElem Foo' allows code to compile but it doesn't work and prints message in console like this: Main.hs:30:10-29: No instance nor default method for class operation Text.StringTemplate.Classes.toSElem - Tried to use same version of HStringTemplate deps (syb was different) - All kinds of desperate messing around (exporting records from modules, changing field names...) - Updated ghc from 7.8.2 to 7.8.4 - Googled error messages to no avail. I hope almighty All would give me some ideas/directions because I have none left. [0] Function: https://github.com/itsuart/fdc_archivist/blob/master/src/HttpUtils.hs#L59 Data: https://github.com/itsuart/fdc_archivist/blob/master/src/ViewModels/HomeView... Usage: https://github.com/itsuart/fdc_archivist/blob/master/src/HomeViewFeature.hs#... -- With best regards, Ilya Seleznev