[Haskell-cafe] Why are these record accesses ambiguous

[Luke Palmer]

On Sat, Jun 6, 2009 at 1:48 AM, John Ky <newhoggy at gmail.com> wrote:

> Hi Haskell Cafe,
>
> In the following code, I get an error saying Ambiguous occurrence `x'.  Why
> can't Haskell work out which x to call based on the type of getA?
>
> Thanks
>
> -John
>
> #!/usr/bin/env runhaskell
>
> > {-# LANGUAGE DisambiguateRecordFields #-}
> > import A
> > import B
> >
> > main = do
> >    let xx = getA
> >    putStrLn $ show x xx


This is parsed as two arguments passed to the show function (which only
takes one argument).

putStrLn $ show (x xx)

Or because putStrLn . show = print;

print $ x xx


>
>
> ----------------------
>
> module A where
>
> data TypeA = TypeA
>    { a :: Int
>    , x :: Int
>    }
>
> getA = TypeA { a = 1, x = 2 }
>
> -------------------------
>
> module B where
>
> data TypeB = TypeB
>    { b :: Int
>    , x :: Int
>    }
>
> getB = TypeB { b = 1, x = 3 }
>
> --------------------------
>
> ./test.lhs:8:21:
>     Ambiguous occurrence `x'
>     It could refer to either `A.x', imported from A at ./test.lhs:3:2-9
>                                       (defined at A.hs:5:5)
>                           or `B.x', imported from B at ./test.lhs:4:2-9
>                                       (defined at B.hs:5:5)
>
>
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