I've noticed a subtle bug with TH. It took me some time to realise what was happening. First I will present my source files. --- [Splices.hs] ---- module Splices where import Char import Language.Haskell.THSyntax debug f = [| do { putStrLn (show ( $(f) + 3)) ; putStrLn "Hello World!" } |] ---------------------------- --- [ Main.hs] --------- module Main where import Language.Haskell.THSyntax import Splices main = $(debug [| (1::Integer) |]) ----------------------------- When I compile this from scratch using the command line: prompt> ghc --make -fglasgow-exts -package haskell-src -package haskell98 Main.hs -o test we get prompt> Chasing modules from: Main.hs Compiling Splices ( Splices.hs, ./Splices.o ) Compiling Main ( Main.hs, ./Main.o ) Loading package base ... linking ... done. Loading package haskell98 ... linking ... done. Loading package haskell-src ... linking ... done. Linking ... And the program works as expected. But I noticed that when I made a small change to Main.hs and recompiled the following would occur: Skipping Splices ( Splices.hs, ./Splices.o ) Compiling Main ( Main.hs, ./Main.o ) Loading package base ... linking ... done. Loading package haskell98 ... linking ... done. Loading package haskell-src ... linking ... done. No instance for (Monad IO) arising from a do statement at <compiler-generated-code> In a right-hand side of function `main': $[splice](debug [| (1 :: Integer) |]) In the definition of `main': main = $[splice](debug [| (1 :: Integer) |]) make: *** [all] Error 1 I can repeat this error at will. As long as Splices.hi and Splices.o are in existence the above error will occur when trying to recompile Main.hs. I was using ghc-5.05.20030118 Sean Seefried