Re: [Haskell-cafe] Read Instance for UArray won't port to linux

14 Mar 2007


      It looks like you forgot to pass a compiler flag, namely -fglasgow-exts.


Cheers,
Spencer Janssen

On Tue, 13 Mar 2007 22:20:20 -0700 (PDT)
SevenThunders  wrote:
...
I have the pleasure of porting a good sized Haskell application to
linux. So far the Haskell code has compiled without incident, however
some code that I hacked
to implement a Read instance for Unboxed Arrays does not compile on
linux even though it compiles just fine on Windows XP in Haskell 6.6.
The code reads as,
instance   Read (UArray Int Double)  where
    readsPrec p = readParen (p > 9)
           (\r -> [(array b as :: UArray Int Double, u) | ("array",s)
<- lex r,
                                     (b,t)       <- reads s,
                                     (as,u)      <- reads t   ])
The error in linux is:
    Illegal instance declaration for `Read (UArray Int Double)'
        (The instance type must be of form (T a b c)
         where T is not a synonym, and a,b,c are distinct type
variables) In the instance declaration for `Read (UArray Int Double)'
Why does it want three parameters for the instance type?  I am
baffled by this.