On Sun, Jun 12, 2011 at 4:00 PM, Alexander Solla
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
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