[M3devel] declaring a type's existance but not enough to instantiate it?
Mika Nystrom
mika at async.caltech.edu
Mon Jan 12 10:34:24 CET 2009
You present it as a true tragic Dilemma.
But isn't there a Third Way---to wit, can't you "Ask the Computer"
to do the work for you?
Generate the code somehow... Parsing the C headers is an obvious
way but there may be others that are simpler, such as writing a
Modula-3 program to generate the cloned M3 headers, sorry, interfaces.
If I had to do this I would use my Scheme interpreter that's coded
in Modula-3 to write a Scheme program to generate the headers. This
program could pull whatever tricks are deemed necessary and suitable,
down to the point of generating and compiling and running C programs
as necessary (or parsing C code, or reading tea leaves). But the
end result would be a set of interfaces written in "Pure Modula-3".
The process of running the header generator would also have very
few dependencies on anything outside the M3 distribution.
Mika
Jay writes:
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>
>This is what you "have to" chose between.
>Header cloning or C code (and C headers).
>=20
>CONST or VAR (or functions?)
>=20
>I'm going to likely make the Uerror change tonight.
>You can still veto it (er=2C vote against it :) )
>=20
>Possibly some convuluted C (enum/#undef)=2C or splitting the Modula-3
>at boundaries that weren't previously believed "natural".
>(See how SetupHandlers is ~two lines in Modula-3 and the rest in C=3B
>this is partly out of ignorance. I don't know how to write those
>two lines in C=3B and laziness=2C I didn't look into how).
>=20
>=20
>=20
>Remember I'm still staying away from mainstream platforms=2C
>so the value isn't what it might appear to be=2C but it is "stage setting"=
>=2C
>and the show might go on. :)
>=20
>=20
>Also=2C the dilemna does get more difficult now=2C with the little C header=
> cloning that remains.
>=20
>For example=2C look at Upthreads.i3.
>Mainly=2C look at function prototypes.
>Constants and types are "known problems".
>Prototypes are gray. They actually tend to be portable.
>=20
>For example:
>=20
>TYPE pid_t =3D INTEGER=3B
><*EXTERNAL "m3_getpid*> PROCEDURE getpid():pid_t=3B
>=20
>or leave it alone?
>getpid is probably the worst example.
>It is so very portable declared in Modula-3.
>But still=2C imagine pid_t might be 16bits or 32 or 64.
>Writing a wrapper is more portable -- as long as the pid isn't stuff into s=
>ome record that the system defines.
>=20
>=20
>Again=2C Upthreads.i3.
>Would you like to see it reduced=2C or left alone?
>Only deal with the types and initializers=2C or also the prototypes?
>You know=2C I could write a little portable layer=2C where all the types ar=
>e pointers=2C always null initialized.
>It would buy /some/ portability=2C and cost some.
>=20
>=20
>Do you like the sem_t change? Partly? Not at all?
>There is one sem_t in the system. So I moved it to be in C code.
>Or=2C as I had it before=2C declared as the max size/align of all the platf=
>orms -- getting that right is the same work as getting it right "the old wa=
>y"=2C except if you make a mistake=2C odds are still good of it being ok.
>=20
>=20
>Should the line be drawn at generating the remaining headers=2C rather than=
> eliminating them?
>Uerror.i3 is easily generated. Good enough?
>=20
>Upthread.i3's types can be generated generally as records with opaque array=
>s with the right size and alignment.
>=20
>Other stuff can be generated or at least checked.
>e.g. to check that getpid is declared correctly=2C you can assign it to a f=
>unction pointer and see if that compiles.
>=20
>Perf on Uerror arguably doesn't matter.
>Is it only error handling code?Or do sockets often go down "error" paths=2C=
> because they are slow and you are waiting for more data?
>=20
>Anyway=2C point is=2C I agree for sure this is valuable=2C but I might be h=
>itting the "tail" of the approach and should switch=2C I'm not sure. I keep=
> saying that though=2C and then press further.
>=20
>=20
> - Jay
>
>
>
>From: hosking at cs.purdue.eduTo: jay.krell at cornell.eduDate: Mon=2C 12 Jan 200=
>9 19:24:50 +1100CC: m3devel at elegosoft.comSubject: Re: [M3devel] declaring a=
> type's existance but not enough to instantiate it?
>
>
>Point taken. We live in a C universe and so need to interact. I do think =
>your work with the headers is useful=2C and I want it to continue. Especia=
>lly in simplifying ports.
>
>
>On 12 Jan 2009=2C at 19:18=2C 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 wi=
>th C code that is described by system-dependent headers=2C or perhaps even =
>fairly system-independent headers outside the Modula-3 tree=2C either write=
> wrapper functions for the functionality in the headers (e.g. stat=2C waitp=
>id)=2C which can be done in a system-independent way=2C or move the Modula-=
>3<->C transition higher=2C which is also usually system-independent=2C e.g.=
> ThreadPThreadC_SetupHandlers. It is either that or clone the headers=2C wh=
>ich seems like the worse evil. There is always going to be a Modula-3<->C t=
>ransition=2C it is just a matter of where it occurs. - Jay
>
>CC: m3devel at elegosoft.comFrom: hosking at cs.purdue.eduTo: jay.krell at cornell.e=
>duSubject: Re: [M3devel] declaring a type's existance but not enough to ins=
>tantiate it?Date: Mon=2C 12 Jan 2009 12:32:15 +1100
>
>
>Jay=2C I really think you are bending over backwards too far just to be abl=
>e to shoe-horn things into C. I *like* having the transpar of C header fil=
>es expressed in Modula-3=2C *particularly* for system calls=2C where you mi=
>ght even be trying to build on a system that does not have the C header fil=
>es installed=2C even though the libraries exist and can be linked to. Fund=
>amentally=2C 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 c=
>onstants to variables.
>
>I am getting very nervous that the changes you are making are destroying th=
>e clarity of the Modula-3 run-time code.
>
>In this particular case=2C you are wanting to use a Modula-3 parameter pass=
>ing mechanism on something that is not declared in Modula-3. Seems kind of=
> dubious to me. Also=2C I really don't like the idea of accessing external=
> variables in C.
>
>-- Tony
>
>On 12 Jan 2009=2C at 11:55=2C Jay wrote:
>
>I considered ADDRESS.However I think it still doesn't satisfy. I want to be=
> able to do this: TYPE Foo_t =3D something=3B<* EXTERNAL *> VAR Foo1=2C Foo=
>2:Foo_t=3B<* EXTERNAL *> PROCEDURE UseFoo(READONLY (* or VAR *) foo:Foo_t)=
>=3B (* Modula-3=2C not external *)PROCEDURE x()=3DBEGIN UseFoo(Foo1)=3B U=
>seFoo(Foo2)=3BEND x=3B AND I want any use of:VAR Foo3:Foo3_t=3B (* Modula-3=
>=2C not external *)to error. This is sem_t and sigset_t in particular. Poss=
>ibly renaming is the thing.They used to be declared in Modula-3=2C system-d=
>ependently=2C butI moved them to portable C. I could remove the types entir=
>ely and change UseFoo to take an address=2Cand declare mask and ackSem to b=
>e integers or I guess.<*EXTERNAL> VAR ackSem : RECORD END=3B That would sat=
>isfy but I thought it might be nicer to still provide the namedtypes to ref=
>er to the external variables. - Jay
>
>From: hosking at cs.purdue.eduTo: jay.krell at cornell.eduDate: Mon=2C 12 Jan 200=
>9 11:13:00 +1100CC: m3devel at elegosoft.comSubject: 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=2C 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=2C at 01:44=2C Jay wrote:
>
>Is there a way in Modula-3 to declare that a type exists=2C and there are <=
>*external*> instances of it=2C without "fully" declaring it=2C so that no M=
>odula-3 can instantiate it? I have done this for sigset_t and sem_t=2C but =
>they could erroneously be instantiated by Modula-3 and I'd like to remove t=
>hat ability to mess up so easily. (* This type is not declared correctly. I=
>t is only instantiated in C code. *) sigset_t =3D RECORD END=3B(* This typ=
>e is not declared correctly. It is only instantiated in C code. *) sem_t =
>=3D RECORD END=3BIn C I believe you can do this=2C like: typedef struct fo=
>o foo_t=3B extern foo_t foo=3B void UseFoo(foo_t*)=3B foo_t* GetFoo=
>(void)=3B Thanks=2C - Jay=
>
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>This is what you "have to" chose between.<BR>
>Header cloning or C code (and C headers).<BR>
> =3B<BR>
>CONST or VAR (or functions?)<BR>
> =3B<BR>
>I'm going to likely make the Uerror change tonight.<BR>
>You can still veto it (er=2C vote against it :) )<BR>
> =3B<BR>
>Possibly some convuluted C (enum/#undef)=2C or splitting the Modula-3<BR>
>at boundaries that weren't previously believed "natural".<BR>
>(See how SetupHandlers is ~two lines in Modula-3 and the rest in C=3B<BR>
>this is partly out of ignorance. I don't know how to write those<BR>
>two lines in C=3B and laziness=2C I didn't look into how).<BR>
> =3B<BR>
> =3B<BR>
> =3B<BR>
>Remember I'm still staying away from mainstream platforms=2C<BR>
>so the value isn't what it might appear to be=2C but it is "stage setting"=
>=2C<BR>
>and the show might go on. :)<BR>
> =3B<BR>
> =3B<BR>
>Also=2C the dilemna does get more difficult now=2C with the little C header=
> cloning that remains.<BR>
> =3B<BR>
>For example=2C look at Upthreads.i3.<BR>
>Mainly=2C look at function prototypes.<BR>
>Constants and types are "known problems".<BR>
>Prototypes are gray. They actually tend to be portable.<BR>
> =3B<BR>
>For example:<BR>
> =3B<BR>
>TYPE pid_t =3D INTEGER=3B<BR>
><=3B*EXTERNAL "m3_getpid*>=3B PROCEDURE getpid():pid_t=3B<BR>
> =3B<BR>
>or leave it alone?<BR>
>getpid is probably the worst example.<BR>
>It is so very portable declared in Modula-3.<BR>
>But still=2C imagine pid_t might be 16bits or 32 or 64.<BR>
>Writing a wrapper is more portable -- as long as the pid isn't stuff into s=
>ome record that the system defines.<BR>
> =3B<BR>
> =3B<BR>
>Again=2C Upthreads.i3.<BR>
>Would you like to see it reduced=2C or left alone?<BR>
>Only deal with the types and initializers=2C or also the prototypes?<BR>
>You know=2C I could write a little portable layer=2C where all the types ar=
>e pointers=2C always null initialized.<BR>
>It would buy /some/ portability=2C and cost some.<BR>
> =3B<BR>
> =3B<BR>
>Do you like the sem_t change? Partly? Not at all?<BR>
>There is one sem_t in the system. So I moved it to be in C code.<BR>
>Or=2C as I had it before=2C declared as the max size/align of all the platf=
>orms -- getting that right is the same work as getting it right "the old wa=
>y"=2C except if you make a mistake=2C odds are still good of it being ok.<B=
>R>
> =3B<BR>
> =3B<BR>
>Should the line be drawn at generating the remaining headers=2C rather than=
> eliminating them?<BR>
>Uerror.i3 is easily generated. Good enough?<BR>
> =3B<BR>
>Upthread.i3's types can be generated generally as records with opaque array=
>s with the right size and alignment.<BR>
> =3B<BR>
>Other stuff can be generated or at least checked.<BR>
>e.g. to check that getpid is declared correctly=2C you can assign it to a f=
>unction pointer and see if that compiles.<BR>
> =3B<BR>
>Perf on Uerror arguably doesn't matter.<BR>
>Is it only error handling code?<BR>Or do sockets often go down "error" path=
>s=2C because they are slow and you are waiting for more data?<BR>
> =3B<BR>
>Anyway=2C point is=2C I agree for sure this is valuable=2C but I might be h=
>itting the "tail" of the approach and should switch=2C I'm not sure. I keep=
> saying that though=2C and then press further.<BR>
> =3B<BR>
> =3B<BR>
> =3B- Jay<BR><BR>
>
><HR id=3DstopSpelling>
<BR>
>From: hosking at cs.purdue.edu<BR>To: jay.krell at cornell.edu<BR>Date: Mon=2C 12=
> Jan 2009 19:24:50 +1100<BR>CC: m3devel at elegosoft.com<BR>Subject: Re: [M3de=
>vel] declaring a type's existance but not enough to instantiate it?<BR><BR>=
><BR>
><DIV><SPAN class=3DEC_Apple-style-span style=3D"WORD-SPACING: 0px=3B FONT: =
>12px Helvetica=3B TEXT-TRANSFORM: none=3B COLOR: rgb(0=2C0=2C0)=3B TEXT-IND=
>ENT: 0px=3B WHITE-SPACE: normal=3B LETTER-SPACING: normal=3B BORDER-COLLAPS=
>E: separate">
><DIV style=3D"WORD-WRAP: break-word"><SPAN class=3DEC_Apple-style-span styl=
>e=3D"WORD-SPACING: 0px=3B FONT: 12px Helvetica=3B TEXT-TRANSFORM: none=3B C=
>OLOR: rgb(0=2C0=2C0)=3B TEXT-INDENT: 0px=3B WHITE-SPACE: normal=3B LETTER-S=
>PACING: normal=3B BORDER-COLLAPSE: separate"><SPAN class=3DEC_Apple-style-s=
>pan style=3D"WORD-SPACING: 0px=3B FONT: 12px Helvetica=3B TEXT-TRANSFORM: n=
>one=3B COLOR: rgb(0=2C0=2C0)=3B TEXT-INDENT: 0px=3B WHITE-SPACE: normal=3B =
>LETTER-SPACING: normal=3B BORDER-COLLAPSE: separate"><SPAN class=3DEC_Apple=
>-style-span style=3D"WORD-SPACING: 0px=3B FONT: 12px Helvetica=3B TEXT-TRAN=
>SFORM: none=3B COLOR: rgb(0=2C0=2C0)=3B TEXT-INDENT: 0px=3B WHITE-SPACE: no=
>rmal=3B LETTER-SPACING: normal=3B BORDER-COLLAPSE: separate"><SPAN class=3D=
>EC_Apple-style-span style=3D"WORD-SPACING: 0px=3B FONT: 12px Helvetica=3B T=
>EXT-TRANSFORM: none=3B COLOR: rgb(0=2C0=2C0)=3B TEXT-INDENT: 0px=3B WHITE-S=
>PACE: normal=3B LETTER-SPACING: normal=3B BORDER-COLLAPSE: separate"><SPAN =
>class=3DEC_Apple-style-span style=3D"WORD-SPACING: 0px=3B FONT: 12px Helvet=
>ica=3B TEXT-TRANSFORM: none=3B COLOR: rgb(0=2C0=2C0)=3B TEXT-INDENT: 0px=3B=
> WHITE-SPACE: normal=3B LETTER-SPACING: normal=3B BORDER-COLLAPSE: separate=
>"><SPAN class=3DEC_Apple-style-span style=3D"WORD-SPACING: 0px=3B FONT: 12p=
>x Helvetica=3B TEXT-TRANSFORM: none=3B COLOR: rgb(0=2C0=2C0)=3B TEXT-INDENT=
>: 0px=3B WHITE-SPACE: normal=3B LETTER-SPACING: normal=3B BORDER-COLLAPSE: =
>separate"><SPAN class=3DEC_Apple-style-span style=3D"WORD-SPACING: 0px=3B F=
>ONT: 12px Helvetica=3B TEXT-TRANSFORM: none=3B COLOR: rgb(0=2C0=2C0)=3B TEX=
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>LLAPSE: separate"><SPAN class=3DEC_Apple-style-span style=3D"WORD-SPACING: =
>0px=3B FONT: 12px Helvetica=3B TEXT-TRANSFORM: none=3B COLOR: rgb(0=2C0=2C0=
>)=3B TEXT-INDENT: 0px=3B WHITE-SPACE: normal=3B LETTER-SPACING: normal=3B B=
>ORDER-COLLAPSE: separate">
><DIV>Point taken.  =3BWe live in a C universe and so need to interact. =
> =3BI do think your work with the headers is useful=2C and I want it to=
> continue.  =3BEspecially in simplifying ports.</DIV>
><DIV><BR></DIV></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></DI=
>V></SPAN></DIV>
><DIV>
><DIV>On 12 Jan 2009=2C at 19:18=2C Jay wrote:</DIV><BR class=3DEC_Apple-int=
>erchange-newline>
><BLOCKQUOTE><SPAN class=3DEC_Apple-style-span style=3D"WORD-SPACING: 0px=3B=
> FONT: 12px Helvetica=3B TEXT-TRANSFORM: none=3B COLOR: rgb(0=2C0=2C0)=3B T=
>EXT-INDENT: 0px=3B WHITE-SPACE: normal=3B LETTER-SPACING: normal=3B BORDER-=
>COLLAPSE: separate">
><DIV class=3DEC_hmmessage style=3D"FONT-SIZE: 10pt=3B FONT-FAMILY: Verdana"=
>>I don't think a development system without C headers is interesting.. Is i=
>t really?<BR> =3B<BR>The transform I apply at times is wherever there i=
>s interaction with C code that is described by system-dependent headers=2C =
>or perhaps even fairly system-independent headers outside the Modula-3 tree=
>=2C either write wrapper functions for the functionality in the headers (e.=
>g. stat=2C waitpid)=2C which =3Bcan be done in a system-independent way=
>=2C =3Bor move the Modula-3<=3B->=3BC transition higher=2C which is=
> also usually system-independent=2C e.g. ThreadPThreadC_SetupHandlers.<BR>&=
>nbsp=3B<BR>It is either that or clone the headers=2C which seems like the w=
>orse evil.<BR> =3B<BR>There is always going to be a Modula-3<=3B->=
>=3BC transition=2C it is just a matter of where it occurs.<BR> =3B<BR>&=
>nbsp=3B- Jay<BR><BR>
><HR id=3DEC_stopSpelling>
><BR>CC:<SPAN class=3DEC_Apple-converted-space> =3B</SPAN><A href=3D"mai=
>lto:m3devel at elegosoft.com">m3devel at elegosoft.com</A><BR>From:<SPAN class=3D=
>EC_Apple-converted-space> =3B</SPAN><A href=3D"mailto:hosking at cs.purdue=
>.edu">hosking at cs.purdue.edu</A><BR>To:<SPAN class=3DEC_Apple-converted-spac=
>e> =3B</SPAN><A href=3D"mailto:jay.krell at cornell.edu">jay.krell at cornell=
>.edu</A><BR>Subject: Re: [M3devel] declaring a type's existance but not eno=
>ugh to instantiate it?<BR>Date: Mon=2C 12 Jan 2009 12:32:15 +1100<BR><BR><B=
>R>
<DIV><SPAN class=3DEC_EC_Apple-style-span style=3D"WORD-SPACING: 0px=3B FON=
>T: 12px Helvetica=3B TEXT-TRANSFORM: none=3B COLOR: rgb(0=2C0=2C0)=3B TEXT-=
>INDENT: 0px=3B WHITE-SPACE: normal=3B LETTER-SPACING: normal=3B BORDER-COLL=
>APSE: separate">
><DIV style=3D"WORD-WRAP: break-word"><SPAN class=3DEC_EC_Apple-style-span s=
>tyle=3D"WORD-SPACING: 0px=3B FONT: 12px Helvetica=3B TEXT-TRANSFORM: none=
>=3B COLOR: rgb(0=2C0=2C0)=3B TEXT-INDENT: 0px=3B WHITE-SPACE: normal=3B LET=
>TER-SPACING: normal=3B BORDER-COLLAPSE: separate"><SPAN class=3DEC_EC_Apple=
>-style-span style=3D"WORD-SPACING: 0px=3B FONT: 12px Helvetica=3B TEXT-TRAN=
>SFORM: none=3B COLOR: rgb(0=2C0=2C0)=3B TEXT-INDENT: 0px=3B WHITE-SPACE: no=
>rmal=3B LETTER-SPACING: normal=3B BORDER-COLLAPSE: separate"><SPAN class=3D=
>EC_EC_Apple-style-span style=3D"WORD-SPACING: 0px=3B FONT: 12px Helvetica=
>=3B TEXT-TRANSFORM: none=3B COLOR: rgb(0=2C0=2C0)=3B TEXT-INDENT: 0px=3B WH=
>ITE-SPACE: normal=3B LETTER-SPACING: normal=3B BORDER-COLLAPSE: separate"><=
>SPAN class=3DEC_EC_Apple-style-span style=3D"WORD-SPACING: 0px=3B FONT: 12p=
>x Helvetica=3B TEXT-TRANSFORM: none=3B COLOR: rgb(0=2C0=2C0)=3B TEXT-INDENT=
>: 0px=3B WHITE-SPACE: normal=3B LETTER-SPACING: normal=3B BORDER-COLLAPSE: =
>separate"><SPAN class=3DEC_EC_Apple-style-span style=3D"WORD-SPACING: 0px=
>=3B FONT: 12px Helvetica=3B TEXT-TRANSFORM: none=3B COLOR: rgb(0=2C0=2C0)=
>=3B TEXT-INDENT: 0px=3B WHITE-SPACE: normal=3B LETTER-SPACING: normal=3B BO=
>RDER-COLLAPSE: separate"><SPAN class=3DEC_EC_Apple-style-span style=3D"WORD=
>-SPACING: 0px=3B FONT: 12px Helvetica=3B TEXT-TRANSFORM: none=3B COLOR: rgb=
>(0=2C0=2C0)=3B TEXT-INDENT: 0px=3B WHITE-SPACE: normal=3B LETTER-SPACING: n=
>ormal=3B BORDER-COLLAPSE: separate"><SPAN class=3DEC_EC_Apple-style-span st=
>yle=3D"WORD-SPACING: 0px=3B FONT: 12px Helvetica=3B TEXT-TRANSFORM: none=3B=
> COLOR: rgb(0=2C0=2C0)=3B TEXT-INDENT: 0px=3B WHITE-SPACE: normal=3B LETTER=
>-SPACING: normal=3B BORDER-COLLAPSE: separate"><SPAN class=3DEC_EC_Apple-st=
>yle-span style=3D"WORD-SPACING: 0px=3B FONT: 12px Helvetica=3B TEXT-TRANSFO=
>RM: none=3B COLOR: rgb(0=2C0=2C0)=3B TEXT-INDENT: 0px=3B WHITE-SPACE: norma=
>l=3B LETTER-SPACING: normal=3B BORDER-COLLAPSE: separate">
><DIV>Jay=2C I really think you are bending over backwards too far just to b=
>e able to shoe-horn things into C.  =3BI *like* having the transpar of =
>C header files expressed in Modula-3=2C *particularly* for system calls=2C =
>where you might even be trying to build on a system that does not have the =
>C header files installed=2C even though the libraries exist and can be link=
>ed to.  =3BFundamentally=2C I think anytime the Modula-3 code is made l=
>ess transparent you should think hard about what you are doing.  =3BThe=
> same with the change of constants to variables.</DIV>
><DIV><BR></DIV>
><DIV>I am getting very nervous that the changes you are making are destroyi=
>ng the clarity of the Modula-3 run-time code.</DIV>
><DIV><BR></DIV>
><DIV>In this particular case=2C you are wanting to use a Modula-3 parameter=
> passing mechanism on something that is not declared in Modula-3.  =3BS=
>eems kind of dubious to me.  =3BAlso=2C I really don't like the idea of=
> accessing external variables in C.</DIV>
><DIV><BR></DIV>
><DIV>-- Tony</DIV></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN><=
>/DIV></SPAN></DIV><BR>
><DIV>
><DIV>On 12 Jan 2009=2C at 11:55=2C Jay wrote:</DIV><BR class=3DEC_EC_Apple-=
>interchange-newline>
><BLOCKQUOTE><SPAN class=3DEC_EC_Apple-style-span style=3D"WORD-SPACING: 0px=
>=3B FONT: 12px Helvetica=3B TEXT-TRANSFORM: none=3B COLOR: rgb(0=2C0=2C0)=
>=3B TEXT-INDENT: 0px=3B WHITE-SPACE: normal=3B LETTER-SPACING: normal=3B BO=
>RDER-COLLAPSE: separate">
><DIV class=3DEC_EC_hmmessage style=3D"FONT-SIZE: 10pt=3B FONT-FAMILY: Verda=
>na">I considered ADDRESS.<BR>However I think it still doesn't satisfy.<BR>&=
>nbsp=3B<BR>I want to be able to do this:<BR> =3B<BR>TYPE =3BFoo_t =
>=3D something=3B<BR><=3B* EXTERNAL *>=3B VAR Foo1=2C Foo2:Foo_t=3B<BR>&=
>lt=3B* EXTERNAL *>=3B PROCEDURE =3BUseFoo(READONLY (* or VAR *) foo:F=
>oo_t)=3B<BR> =3B<BR>(* Modula-3=2C not external *)<BR>PROCEDURE x()=3D<=
>BR>BEGIN<BR> =3B UseFoo(Foo1)=3B<BR> =3B UseFoo(Foo2)=3B<BR>END x=
>=3B<BR> =3B<BR>AND I want any use of:<BR>VAR Foo3:Foo3_t=3B (* Modula-3=
>=2C not external *)<BR><BR>to error. This is sem_t and sigset_t in particul=
>ar.<BR> =3B<BR>Possibly renaming is the thing.<BR>They used to be decla=
>red in Modula-3=2C system-dependently=2C but<BR>I moved them to portable C.=
><BR> =3B<BR>I could remove the types entirely and change UseFoo to take=
> an address=2C<BR>and declare mask and ackSem to be integers or I guess.<BR=
>><=3B*EXTERNAL>=3B VAR ackSem =3B: RECORD END=3B<BR> =3B<BR>Tha=
>t would satisfy but I thought it might be nicer to still provide the named<=
>BR>types to refer to the external variables.<BR> =3B<BR> =3B- Jay<B=
>R><BR>
><HR id=3DEC_EC_stopSpelling>
><BR>From:<SPAN class=3DEC_EC_Apple-converted-space> =3B</SPAN><A href=
>=3D"mailto:hosking at cs.purdue.edu">hosking at cs.purdue.edu</A><BR>To:<SPAN cla=
>ss=3DEC_EC_Apple-converted-space> =3B</SPAN><A href=3D"mailto:jay.krell=
>@cornell.edu">jay.krell at cornell.edu</A><BR>Date: Mon=2C 12 Jan 2009 11:13:0=
>0 +1100<BR>CC:<SPAN class=3DEC_EC_Apple-converted-space> =3B</SPAN><A h=
>ref=3D"mailto:m3devel at elegosoft.com">m3devel at elegosoft.com</A><BR>Subject: =
>Re: [M3devel] declaring a type's existance but not enough to instantiate it=
>?<BR><BR>What's wrong with using ADDRESS for references to opaque values? &=
>nbsp=3BIf sigset_t is never instantiated in Modula-3=2C then why do you nee=
>d it declared there?<BR>
><DIV><BR>
><DIV><SPAN class=3DEC_EC_EC_Apple-style-span style=3D"WORD-SPACING: 0px=3B =
>FONT: 12px Helvetica=3B TEXT-TRANSFORM: none=3B COLOR: rgb(0=2C0=2C0)=3B TE=
>XT-INDENT: 0px=3B WHITE-SPACE: normal=3B LETTER-SPACING: normal=3B BORDER-C=
>OLLAPSE: separate">
><DIV style=3D"WORD-WRAP: break-word"><SPAN class=3DEC_EC_EC_Apple-style-spa=
>n style=3D"WORD-SPACING: 0px=3B FONT: 12px Helvetica=3B TEXT-TRANSFORM: non=
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>TTER-SPACING: normal=3B BORDER-COLLAPSE: separate"><SPAN class=3DEC_EC_EC_A=
>pple-style-span style=3D"WORD-SPACING: 0px=3B FONT: 12px Helvetica=3B TEXT-=
>TRANSFORM: none=3B COLOR: rgb(0=2C0=2C0)=3B TEXT-INDENT: 0px=3B WHITE-SPACE=
>: normal=3B LETTER-SPACING: normal=3B BORDER-COLLAPSE: separate"><SPAN clas=
>s=3DEC_EC_EC_Apple-style-span style=3D"WORD-SPACING: 0px=3B FONT: 12px Helv=
>etica=3B TEXT-TRANSFORM: none=3B COLOR: rgb(0=2C0=2C0)=3B TEXT-INDENT: 0px=
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>OLLAPSE: separate"><SPAN class=3DEC_EC_EC_Apple-style-span style=3D"WORD-SP=
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>TER-SPACING: normal=3B BORDER-COLLAPSE: separate"><SPAN class=3DEC_EC_EC_Ap=
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>RANSFORM: none=3B COLOR: rgb(0=2C0=2C0)=3B TEXT-INDENT: 0px=3B WHITE-SPACE:=
> normal=3B LETTER-SPACING: normal=3B BORDER-COLLAPSE: separate"><SPAN class=
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>ate">
><DIV><FONT class=3DEC_EC_EC_Apple-style-span color=3D#0000ff><FONT class=3D=
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>AN class=3DEC_EC_EC_Apple-style-span style=3D"COLOR: rgb(0=2C0=2C255)=3B FO=
>NT-FAMILY: 'Gill Sans'">Antony Hosking</SPAN></SPAN></FONT></FONT><FONT cla=
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>=3DEC_EC_EC_Apple-style-span style=3D"FONT-FAMILY: 'Gill Sans'"> =3B| C=
>omputer Science | Purdue University</SPAN></SPAN></FONT></DIV>
><DIV><FONT class=3DEC_EC_EC_Apple-style-span face=3DGillSans-Light><SPAN cl=
>ass=3DEC_EC_EC_Apple-style-span style=3D"FONT-FAMILY: GillSans-Light">305 N=
>. University Street | West Lafayette | IN 47907 | USA</SPAN></FONT></DIV>
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>ht"> =3B+1 765 494 6001 |<SPAN class=3DEC_EC_Apple-converted-space>&nbs=
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>AN></DIV></SPAN></DIV><BR>
><DIV>
><DIV>On 12 Jan 2009=2C at 01:44=2C Jay wrote:</DIV><BR class=3DEC_EC_EC_App=
>le-interchange-newline>
><BLOCKQUOTE><SPAN class=3DEC_EC_EC_Apple-style-span style=3D"WORD-SPACING: =
>0px=3B FONT: 12px Helvetica=3B TEXT-TRANSFORM: none=3B COLOR: rgb(0=2C0=2C0=
>)=3B TEXT-INDENT: 0px=3B WHITE-SPACE: normal=3B LETTER-SPACING: normal=3B B=
>ORDER-COLLAPSE: separate">
><DIV class=3DEC_EC_EC_hmmessage style=3D"FONT-SIZE: 10pt=3B FONT-FAMILY: Ve=
>rdana">Is there a way in Modula-3 to declare that =3Ba type exists=2C a=
>nd there are <=3B*external*>=3B instances of it=2C without "fully" decl=
>aring it=2C so that no Modula-3 can instantiate it?<BR> =3B<BR>I have d=
>one this for sigset_t and sem_t=2C but they could erroneously be instantiat=
>ed by Modula-3 and I'd like to remove that ability to mess up so easily.<BR=
>> =3B<BR>(* This type is not declared correctly. It is only instantiate=
>d in C code. *)<BR> =3B sigset_t =3D RECORD END=3B<BR><BR>(* This type =
>is not declared correctly. It is only instantiated in C code. *)<BR> =
>=3B sem_t =3D RECORD END=3B<BR><BR>In C I believe you can do this=2C like:<=
>BR> =3B =3Btypedef struct foo foo_t=3B =3B<SPAN class=3DEC_EC_E=
>C_Apple-converted-space> =3B</SPAN><BR> =3B =3Bextern foo_t foo=
>=3B =3B<SPAN class=3DEC_EC_EC_Apple-converted-space> =3B</SPAN><BR>=
> =3B<BR> =3Bvoid UseFoo(foo_t*)=3B<SPAN class=3DEC_EC_EC_Apple-conv=
>erted-space> =3B</SPAN><BR> =3B foo_t* GetFoo(void)=3B<SPAN class=
>=3DEC_EC_EC_Apple-converted-space> =3B</SPAN><BR> =3B<BR>Thanks=2C<=
>BR> =3B- Jay<BR><BR><BR><BR></DIV></SPAN></BLOCKQUOTE></DIV><BR></DIV><=
>/DIV></SPAN><BR class=3DEC_EC_Apple-interchange-newline></BLOCKQUOTE></DIV>=
><BR></DIV></SPAN><BR class=3DEC_Apple-interchange-newline></BLOCKQUOTE></DI=
>V><BR></body>
></html>=
>
>--_6117a048-9185-4c03-badb-ef8f93402268_--
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