Haskell: "Not in scope: '>>'" with no implicit prelude

Question

Compiling the following Haskell program with GHC 6.12.1 yields an error:

{-# LANGUAGE NoImplicitPrelude #-}

module Example where

import Prelude(Integer, fromInteger, (==))

f :: Integer -> Integer
f n
    | n == 0 = 0

Namely:

example.hs:9:6: Not in scope: `>>'

The error goes away when I change the import statement to:

import Prelude(Integer, fromInteger, (==), (>>))

This makes sense. What I don't understand, however, why there is an error in the first place. My program doesn't seem to make use of any Monad, while >> is one of the Monad operators.

That's weird! I've added a nonsense definition like (>>) = "blah" and it still typechecks and works as expected; (>>) isn't called at all, as far as I can tell. For what it's worth, your first version works unmodified in GHC 7.0.2. — yatima2975

Marat Salikhov Marat Salikhov · Accepted Answer · 2011-03-23T10:09:26

I don't know the root cause of this problem, but if you compile your code with -ddump-rn-trace option on, you can see that the compiler for some reason puts (>>) into a list of definitions used, something like that:

    finish Dus [(Nothing, [(314, Integer)]),
            (Just [(rdd, f)], [(01D, >>), (01E, fromInteger), (01L, ==)]),
            (Nothing, [])]

Most certainly it is a bug in GHC 6.12.1

Haskell: "Not in scope: '>>'" with no implicit prelude

3 Answers