Restricted Types and Infinite Loops

[Keean Schupke]

I seem to remember that if you define the class:

class DictXMLData h => XMLData h ...

instance (Data d a,XMLNamespace a) => XMLData d where ...

then providing you annotate the instance functions with the relavent
scoped type variables (d and a) then the compiler will infer XMLNamespace
correctly for those instances that use it from the XMLData constraint.

    Keean.

Simon David Foster wrote:

>On Fri, 2005-02-18 at 02:18 +0100, Ralf Laemmel wrote:
>
>  
>
>>Here I assume that you don't _really_ depend on ClassB to be a 
>>superclass of ClassA. (Why would you?)
>>    
>>
>
>Ok, here's what the real class head is (or was before I butchered it to
>make it work);
>
>class (Data (DictXMLData h) a, XMLNamespace a) => XMLData h a where
>
>We want to do this so that it is unnecessary to store XML Namespaces in
>the XMLData instances (which is supposed to be for only encoding). There
>are two reasons why this is necessary;
>
>* 1 - We have another class XSDType a, which gives types an XSD Type.
>This also depends on the types having a namespace. If we don't have this
>class dependency, we end up with repeated data.
>* 2 - In various contexts, you will require a different namespace for a
>particular element, but the same encoder. For example, when creating a
>SOAP Envelope, the "int" data-type could have the SOAP Encoding
>namespace or it could have the XSD Namespace. Further it may not have a
>namespace at all, in which case the default instance (XMLNamespace a)
>will take over. By taking the dependency out you bind a particular
>namespace to an encoder.
>
>For now, the various encoders for XSD data-types are in the XSD Module,
>this means that any user that wants to encode an int or string must
>import the XSD module, since we can't centralise the encoder.
>
>  
>
>>This is a simpler recursion scheme in terrms of class/instance constraints.
>>    
>>
>
>Maybe, but sadly it doesn't achieve my goal. I could do Namespaces via a
>hook, but that makes the construction and encoding of namespace tables
>almost impossible.
>
>Thanks,
>
>-Si.
>
>  
>