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

[Simon Peyton-Jones]

Ah, a fine idea.  I'll do that anyway; maybe others will have even better ideas, but that's a good start

S

| -----Original Message-----
| From: haskell-cafe-bounces at haskell.org [mailto:haskell-cafe-bounces at haskell.org] On Behalf Of Björn
| Bringert
| Sent: 14 March 2007 14:28
| To: Simon Peyton-Jones
| Cc: haskell-cafe at haskell.org
| Subject: Re: [Haskell-cafe] Read Instance for UArray won't port to linux
|
| Simon Peyton-Jones wrote:
| > | 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.
| >
| > It's saying that in Haskell 98 you can have
| >         instance Read (UArray a b)
| > (for type variables a, b) but not
| >         instance Read (UArray Int Double)
| >
| > (As Spencer says, use -fglasgow-exts to lift the H98 restriction.)
| >
| > However, you mis-read the error message to say "the instance type must have three parameters", which
| isn't what I meant at all!  I was trying to use an example of the general form, but conveyed the wrong
| idea.
| >
| > I can see why you read it that way.  Now you understand, can you give me a better error message?
|
| I'm not the original poster, but what about just changing it to "The
| instance type must be of the form (T a1 ... an) where T is not a
| synonym, and a1 ... an are distinct type variables)"?
|
| /Björn
| _______________________________________________
| Haskell-Cafe mailing list
| Haskell-Cafe at haskell.org
| http://www.haskell.org/mailman/listinfo/haskell-cafe