This module adds an Eq instance for Parsec's ParseError type if it's needed. Import by using (since this module only provides instances):

import Text.ParseErrorEq ()

For reference, Parsec 3.1.9 adds the Eq instance, in the commit here:

https://github.com/aslatter/parsec/commit/3fb40aaa683fd90f3f0dd9f3c32c6ba707fb24b1