Re: [Caml-list] Bug in the module system of version 3.12.0+beta1

[Dumitru Potop-Butucaru <dumitru.potop_butucaru@inria.fr>]

[-- Attachment #1: Type: text/plain, Size: 3373 bytes --]


Ok, I got it.

Thank you all for the help,
Jacky

On 22/07/2010 08:47, Jacques Garrigue wrote:
> No, I'm saying that this kind of syntax overloading occurs in Haskell.
> However, since Haskell has no functors, you cannot do that either.
>
> Again, what you ask for is possible in ocaml, and in a particularly clean
> way in 3.12.  Namely, Jeremy Yallop's second example does exactly what you want.
> The only difference is the syntax: you write "ABC with module M := IntList"
> rather than "ABC(IntList)". Different concepts get different syntax.
>
> Jacques
>
> On 2010/07/22, at 15:38, Dumitru Potop-Butucaru wrote:
>
>    
>> So, what you say is that this way of manipulating
>> module types can be done in Haskell?
>>
>> Yours,
>> Jacky
>>
>>
>> On 22/07/2010 08:18, Jacques Garrigue wrote:
>>      
>>> From: Dumitru Potop-Butucaru<dumitru.potop_butucaru@inria.fr>
>>>
>>>        
>>>> However, I still did not understand this statement of
>>>> Jeremy Yallop:
>>>>
>>>>          
>>>>>> module type Abc =
>>>>>>     functor (M:Simple) ->
>>>>>>     sig
>>>>>>        val x : M.t
>>>>>>     end
>>>>>>
>>>>>>
>>>>>>              
>>>>> You're trying to treat Abc as a functor from signatures to signatures
>>>>> (i.e. as a parameterised signature). In fact, it's something quite
>>>>> different: it's the *type* of a functor from structures to structures.
>>>>>
>>>>>
>>>>>            
>>>> If I understand well, what I try to do is impossible for
>>>> some deep theoretical reason. Can someone explain this
>>>> to me, or point me to a relevant paper explaining it?
>>>>
>>>>          
>>> I think this is not a question of impossibility, rather of
>>> misunderstanding of the relation between modules and signatures.
>>> A module type describes modules, it does not replace them.
>>> In particular, in another mail you asked for the construct:
>>>
>>>    module type MyModuleType(Param:ParamType) = sig ... end
>>>
>>> But this just doesn't make sense. The type of a functor is not a
>>> functor between module types. Just like the type "t1 * t2" describes
>>> pairs of values of type t1 and t2, but it is not itself a pair of
>>> types, but rather a product.
>>>
>>> Note of course that one might want to play on the conceptual
>>> similarity to write the two in the same way. Haskell does that a lot,
>>> writing (t1,t2) for the product of the types t1 and t2. But if
>>> you look at languages like Coq, where types are also values, this
>>> kind of overloading seems dangerous.
>>>
>>> Another similar misunderstanding is when you write
>>>        include Abc(module type of IntSet)
>>> This statement is doubly wrong: first you cannot apply a module type,
>>> but even if Abc were a functor, it could only be applied to a module,
>>> not a module type.
>>> Others have explained how you can do what you intended, in two
>>> different ways.
>>> The classical way is to use a real functor, returning a signature
>>> enclosed in a module, since there is no way to return a signature
>>> alone. There is nothing against applying functors inside signatures.
>>> The new solution in 3.12 is to use a variant of the "with"
>>> construct, which does exactly what you want, i.e. it turns a
>>> signature into a "function" returning a signature.
>>>
>>> Hope this helps,
>>>
>>> Jacques Garrigue
>>>
>>>
>>>
>>>        
>> <dumitru_potop_butucaru.vcf>
>>      
>
>
>    


[-- Attachment #2: dumitru_potop_butucaru.vcf --]
[-- Type: text/x-vcard, Size: 335 bytes --]

begin:vcard
fn:Dumitru Potop-Butucaru
n:Potop-Butucaru;Dumitru
org:INRIA Rocquencourt;Project AOSTE
adr:;;Domaine de Voluceau, BP 105;Le Chesnay;;F-78153;France
email;internet:dumitru.potop_butucaru@inria.fr
tel;work:+33-139.63.55.80
tel;fax:+33-139.63.51.93
x-mozilla-html:FALSE
url:http://www.DumitruPotop.net
version:2.1
end:vcard