[pypy-dev] Custom types for annotating a flow object space

[Henry Gomersall]

On 22/03/15 21:45, Ronan Lamy wrote:
>>
>> My question then regards the following. MyHDL represents certain low
>> level structures as python objects. For example, there is a notion of a
>> signal, represented by a Signal object, that has a one to one mapping to
>> the target HDL language. All the attributes of the Signal object
>> describe how it should be converted. So, during annotation, the Signal
>> object should be maintained as a base type, rather than burying deeper
>> into the object to try and infer more about its type (which invariably
>> breaks things due to RPython non-conformity). There are probably a few
>> other types (though not many) that should be handled similarly.
>>
>> How does one instruct the translator to do this? Is it a case of writing
>> a custom TranslationDriver to handle the custom types?
>
> No, you simply need to register your Python types with the translator 
> and describe their properties by subclassing some internal classes.
> The interface is a bit complicated and requires some understanding of 
> RPython's inner workings, but it works. rply has a good example of 
> that: https://github.com/alex/rply/blob/master/rply/lexergenerator.py 
> (specifically, the part that is guarded by 'if rpython:')
>
> Here's how it works:
> The ExtRegistryEntry tells the annotator to special-case Rule objects 
> by annotating them as SomeRule(). SomeRule describes the 
> annotator-level properties of Rule objects while RuleRepr tells the 
> rtyper how to translate them to low-level (C-like) objects.
>
> In your case, you definitely need an ExtRegistryEntry and a 
> SomeSignal, but what to put in SignalRepr and whether you even need it 
> depends on how you intend the Verilog/VHDL backend to work. 

Ah, that's fantastic :)

So as I understand it, ExtRegistryEntry provides some metaclass magic 
that auto registers the relevant type as a special case, with the 
decision made by the object returned from compute_annotation() ?

Is there some documentation on this aspect of the internals from 
RPython? There are obviously lots of questions that would be much easier 
to get with some docs (ordering? default actions? what the default 
methods are doing?).

Thanks!
Henry