[Haskell] Signature error because the order

Martijn van Steenbergen martijn at van.steenbergen.nl
Thu Jan 14 07:24:16 EST 2010

Hi Luis,

Luis Cabellos wrote:
> But if I change the order of *Show* and *Num* in the signature of 
> /prettyShow/ it works.
> It's a GHC problem? it's normal than signature is order-dependent?

I think this is on purpose. The error specifically says that the 
contexts must be identical (rather than containing the same classes in 
arbitrary). I suspect this is how Haskell98 has specified it.

If you enable the RelaxedPolyRec language extension, this restriction no 
longer applies and your code compiles fine.

Hope this helps,


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