Maude-help mailing list

[Michael Katelman <katelman AT uiuc.edu>]

At least regarding sorts, which you mentioned, that is part of the
object theory and doesn't require going to the meta-level:

cmb t1 : A if t2 : B .

does not require the meta-level to ask the question about t2 being of
sort B. So, something like type introspection exists without
implicit/explicit loading of META-LEVEL.

-Mike


On Mon, Apr 11, 2011 at 6:19 AM, Francisco Durán 
<duran AT lcc.uma.es>
 wrote:
> Hi Pat,
>
> The META-LEVEL module provides key sorts (like Term and Module) and key 
> functionality (operations like metaReduce or metaRewrite) which facilitate 
> access to the metalevel of Maude. Asking whether we can access Maude's 
> metalevel without the META-LEVEL module is like asking whether we can have 
> access to Java's metalevel without the Class class. Well, it must be there, 
> loaded in the system, although you don't really need to name it.
>
> The getClass method to get the Class object is like using upModule to get 
> the metarepresentation of the module. To get "things" from this module, or 
> from terms in that module, you can use functions in the META-LEVEL module 
> or define your own ones.
>
> Can I get the sort of a data item? Let me use my FOO module again:
>
> reduce leastSort(upModule('FOO, false), upTerm(f(true))) .
>
> Of course, for this command to be evaluated it has to be in the context of 
> a module importing both META-LEVEL and the FOO module, my BAR module.
>
> The result is
>
> result Sort: 'Bar
>
> Cheers,
>
> Francisco
>
> El 11/04/2011, a las 11:09, Patrick Browne escribió:
>
>> Francisco,
>> In OO languages, such as Java, the term reflection means that a program
>> can access information about objects (e.g. find its class at runtime). I
>> wish to know whether MEL can perform a similar task in Maude (i.e. find
>> the sort of a data item). Can MEL alone without explicit reference to
>> META-LEVEL provide this type of reflection?
>>
>> My motivation is that I need to know precisely how this OO style
>> reflection is done in Maude.
>>
>> Pat
>>
>> On 10/04/2011 22:30, Francisco Durán wrote:
>>> Hi Pat,
>>>
>>> I'm not sure whether there is something more behind your question, I 
>>> don't get that of "the kind and object level", but I would say that the 
>>> answer is yes, almost everything in Maude is reflected, and can be used 
>>> at Maude's metalevel.
>>>
>>> fmod FOO is
>>>  sorts Foo Bar .
>>>  subsort Bar < Foo .
>>>  op f : Bool -> Foo .
>>>  var B : Bool .
>>>  cmb f(B) : Bar if B .
>>> endfm
>>>
>>> fmod BAR is inc FOO + META-LEVEL . endfm
>>>
>>> red metaReduce(upModule('FOO, false), upTerm(f(true))) .
>>>
>>> Francisco
>>
>>
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>
>
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