On Sun, Jun 12, 2011 at 4:00 PM, Alexander Solla <alex.so...@gmail.com> wrote: > Hi everybody, > I'm having a bit of a problem with Parsec. The most relevant error message > is: > Couldn't match expected type `Text.Parsec.Prim.ParsecT > String () > Control.Monad.Identity.Identity String' > against inferred type > `parsec-2.1.0.1:Text.ParserCombinators.Parsec.Prim.Parser > [Char]' > In the expression: countMinMax ... > So apparently, the module/package that defines countMinMax and the current > module are using different versions of Parsec. My global GHC database has > Parsec 3.1.1 installed, but each package has the constraint > parsec >=2.1 && <2.2 > Both modules use the exact same import line: > import Text.ParserCombinators.Parsec -- Lime.Data.IPAddress > import Text.ParserCombinators.Parsec -- Lime.Utility.Parsec > countMinMax :: (Integral n) => n -> n -> Parser a -> Parser [a] > and > the expression GHC is complaining about above has type Parser String. > The cabal-dev package database contains only one version of Parsec: > parsec-2.1.0.1-190ec41e7316b7eb7fddf355acddd826.conf > What's going on here?
Types from differing versions of the same module are specifically not compatible - even if they are defined identically (in this case they are different, though). You can do one of two things: 1. Edit the package description of the package that wants the older version of parsec to allow to use the new one. Also, it helps to slightly bump the version number of the package when you do this. 2. Use the older version of parsec in your software. You already have it installed (or else the package you want to use wouldn't be able to load!). If you're using ghci you can start it with the option '-package parsec-2.1.0.1'. Antoine > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
