Dear GHCers, I have been experimenting some more with environments for lab work for an FP intro course. One thing students tend to have difficulty with in the initial labs are the error messages including type classes, or any kind of more general type than they expected. I am trying to work around this, by supplying a "Number" type for the first lab and gradually increasing the complexity over the next few labs. To let all error messages be in terms of my type, I use the NoImplicitPrelude option in a LANGUAGE pragma. However, I find the behaviour of GHCi unexpected. I have reduced the problem to a small case that reproduces the bug. Here is my BugDemo module: {-# LANGUAGE NoImplicitPrelude #-} module BugDemo where import qualified Prelude as P newtype Number = N P.Integer fromInteger = N Look at the following sessions: [holzensp@ewi1043:work/FPPrac]% ghci BugDemo.hs GHCi, version 6.12.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package ffi-1.0 ... linking ... done. [1 of 1] Compiling BugDemo ( BugDemo.hs, interpreted ) Ok, modules loaded: BugDemo. *BugDemo> 5 5 *BugDemo> :t 5 5 :: (P.Num t) => t *BugDemo> :q Leaving GHCi. [holzensp@ewi1043:work/FPPrac]% ghci -fno-implicit-prelude BugDemo.hs GHCi, version 6.12.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package ffi-1.0 ... linking ... done. [1 of 1] Compiling BugDemo ( BugDemo.hs, interpreted ) on the commandline: Warning: -fno-implicit-prelude is deprecated: use -XNoImplicitPrelude or pragma {-# LANGUAGE NoImplicitPrelude #-} instead Ok, modules loaded: BugDemo. *BugDemo> 5 <interactive>:1:0: Not in scope: `>>' *BugDemo> :t 5 5 :: Number *BugDemo> It's a bit awkward that I get an explicit warning about -fno-implicit-prelude being deprecated, while the behaviour is actually different. Obviously, when leaving out the definition for fromInteger, the second session fails whenever I type a number, whereas the first session behaves the same way. This seems to be me to be a bug. Kind regards, Philip