[M3devel] declaring a type's existance but not enough to instantiate it?

[Tony Hosking]

Point taken.  We live in a C universe and so need to interact.  I do  
think your work with the headers is useful, and I want it to  
continue.  Especially in simplifying ports.

On 12 Jan 2009, at 19:18, Jay wrote:

> I don't think a development system without C headers is  
> interesting.. Is it really?
>
> The transform I apply at times is wherever there is interaction with  
> C code that is described by system-dependent headers, or perhaps  
> even fairly system-independent headers outside the Modula-3 tree,  
> either write wrapper functions for the functionality in the headers  
> (e.g. stat, waitpid), which can be done in a system-independent way,  
> or move the Modula-3<->C transition higher, which is also usually  
> system-independent, e.g. ThreadPThreadC_SetupHandlers.
>
> It is either that or clone the headers, which seems like the worse  
> evil.
>
> There is always going to be a Modula-3<->C transition, it is just a  
> matter of where it occurs.
>
>  - Jay
>
>
> CC: m3devel at elegosoft.com
> From: hosking at cs.purdue.edu
> To: jay.krell at cornell.edu
> Subject: Re: [M3devel] declaring a type's existance but not enough  
> to instantiate it?
> Date: Mon, 12 Jan 2009 12:32:15 +1100
>
>
> Jay, I really think you are bending over backwards too far just to  
> be able to shoe-horn things into C.  I *like* having the transpar of  
> C header files expressed in Modula-3, *particularly* for system  
> calls, where you might even be trying to build on a system that does  
> not have the C header files installed, even though the libraries  
> exist and can be linked to.  Fundamentally, I think anytime the  
> Modula-3 code is made less transparent you should think hard about  
> what you are doing.  The same with the change of constants to  
> variables.
>
> I am getting very nervous that the changes you are making are  
> destroying the clarity of the Modula-3 run-time code.
>
> In this particular case, you are wanting to use a Modula-3 parameter  
> passing mechanism on something that is not declared in Modula-3.   
> Seems kind of dubious to me.  Also, I really don't like the idea of  
> accessing external variables in C.
>
> -- Tony
>
> On 12 Jan 2009, at 11:55, Jay wrote:
>
> I considered ADDRESS.
> However I think it still doesn't satisfy.
>
> I want to be able to do this:
>
> TYPE Foo_t = something;
> <* EXTERNAL *> VAR Foo1, Foo2:Foo_t;
> <* EXTERNAL *> PROCEDURE UseFoo(READONLY (* or VAR *) foo:Foo_t);
>
> (* Modula-3, not external *)
> PROCEDURE x()=
> BEGIN
>   UseFoo(Foo1);
>   UseFoo(Foo2);
> END x;
>
> AND I want any use of:
> VAR Foo3:Foo3_t; (* Modula-3, not external *)
>
> to error. This is sem_t and sigset_t in particular.
>
> Possibly renaming is the thing.
> They used to be declared in Modula-3, system-dependently, but
> I moved them to portable C.
>
> I could remove the types entirely and change UseFoo to take an  
> address,
> and declare mask and ackSem to be integers or I guess.
> <*EXTERNAL> VAR ackSem : RECORD END;
>
> That would satisfy but I thought it might be nicer to still provide  
> the named
> types to refer to the external variables.
>
>  - Jay
>
>
> From: hosking at cs.purdue.edu
> To: jay.krell at cornell.edu
> Date: Mon, 12 Jan 2009 11:13:00 +1100
> CC: m3devel at elegosoft.com
> Subject: Re: [M3devel] declaring a type's existance but not enough  
> to instantiate it?
>
> What's wrong with using ADDRESS for references to opaque values?  If  
> sigset_t is never instantiated in Modula-3, then why do you need it  
> declared there?
>
> Antony Hosking | Associate Professor | Computer Science | Purdue  
> University
> 305 N. University Street | West Lafayette | IN 47907 | USA
> Office +1 765 494 6001 | Mobile +1 765 427 5484
>
>
>
> On 12 Jan 2009, at 01:44, Jay wrote:
>
> Is there a way in Modula-3 to declare that a type exists, and there  
> are <*external*> instances of it, without "fully" declaring it, so  
> that no Modula-3 can instantiate it?
>
> I have done this for sigset_t and sem_t, but they could erroneously  
> be instantiated by Modula-3 and I'd like to remove that ability to  
> mess up so easily.
>
> (* This type is not declared correctly. It is only instantiated in C  
> code. *)
>   sigset_t = RECORD END;
>
> (* This type is not declared correctly. It is only instantiated in C  
> code. *)
>   sem_t = RECORD END;
>
> In C I believe you can do this, like:
>   typedef struct foo foo_t;
>   extern foo_t foo;
>
>  void UseFoo(foo_t*);
>   foo_t* GetFoo(void);
>
> Thanks,
>  - Jay
>
>
>
>
>
>
>

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