I have observed the following weird behavior: When I define an instance of a certain MPTC in a separate module from the definition of the class, ghci's ability to recognize the methods of the class seems to vary depending on whether or not hi files exist for the modules. I am using the current Debian build of GHC 6.6. Below are a set of three files that reproduce the behavior, and a shell session that demonstrates it. Before I compile the program, ghci works fine. After I compile with ghc - thus generating hi files - ghci gets confused. Then I delete the hi files and everything is fine again. Thanks, Yitz -- File Oops.hs {-# OPTIONS_GHC -fglasgow-exts #-} module Oops where class Oops a b c | a -> b c where foo :: a -> b -> a -- File Whoops.hs {-# OPTIONS_GHC -fglasgow-exts #-} module Whoops where import Oops instance Oops String Int Bool where foo x n = show (x, n) -- File runWhoops.hs module Main where import Whoops import Oops main = putStrLn $ foo "bar" 42 $ ghci Whoops / /_\// /_/ / / | | GHC Interactive, version 6.6, for Haskell 98. Loading package base ... linking ... done. [1 of 2] Compiling Oops ( Oops.hs, interpreted ) [2 of 2] Compiling Whoops ( Whoops.hs, interpreted ) Ok, modules loaded: Oops, Whoops. *Whoops> foo "baz" 7 "(\"baz\",7)" *Whoops> Leaving GHCi. $ ghc --make runWhoops.hs [1 of 3] Compiling Oops ( Oops.hs, Oops.o ) [2 of 3] Compiling Whoops ( Whoops.hs, Whoops.o ) [3 of 3] Compiling Main ( runWhoops.hs, runWhoops.o ) Linking runWhoops ... $ ghci Whoops / /_\// /_/ / / | | GHC Interactive, version 6.6, for Haskell 98. Loading package base ... linking ... done. Ok, modules loaded: Oops, Whoops. Prelude Whoops> foo "baz" 7 <interactive>:1:0: Not in scope: `foo' Prelude Whoops> Leaving GHCi. $ rm *.hi $ ghci Whoops / /_\// /_/ / / | | GHC Interactive, version 6.6, for Haskell 98. Loading package base ... linking ... done. [1 of 2] Compiling Oops ( Oops.hs, interpreted ) [2 of 2] Compiling Whoops ( Whoops.hs, interpreted ) Ok, modules loaded: Oops, Whoops. *Whoops> foo "baz" 7 "(\"baz\",7)"