External, C, AsmName, ...

Hello folks,

(* This mail is somehow long. In short: I want to take the directives `Extern', `C', and `AsmName' *out* of GPC and extend the syntax of `External' instead. Okay? :*)

as you know (?;-), we have the directives `External', `Extern' (same as `External'), `C', and `AsmName' in GPC for specifying external procedures. This is especially useful when using libraries written in C, for example:

Procedure Foo; External; (* yields "Foo" *)

Procedure ioCtl ( FilDes, Cmd: Integer; ... ); C; (* yields "ioctl" *)

Procedure XOpenDisplay ( Name: __CString__ ); AsmName 'XOpenDisplay';

This turned out not to be enough; we need the same for variables. Actually we already have

Var Foo: __external__ Integer; (* yields "foo", not "Foo"! *)

but this does not cover cases where the external variable needs a name with a capital letter.

As an intermediate solution, I implemented

Var Foo: __asmname__ 'foO' Integer;

(patched source is available on demand), but I think it is not the best way to implement these things.

Now I am looking out for reasonable ideas.

Does somebody know what the ISO/ANSI Standards say about this?

My own thoughts follow.

I would suggest to define as few directives as possible and to drop everything but `External' but extend its syntax to meet our requirements. A first approach could be

Procedure foo; external; (* yields "Foo" *)

Var x: Integer; external; (* yields "X" *)

and

Procedure foo; external 'foO';

Var x: Integer; external 'my_x';

but it would crash with Borland Pascal's use of `External' where the latter declaration would mean that Procedure foo is contained in a shared library named `foO'.

Okay, so let's stay for the moment at Borland's syntax. In the same context they also define

Procedure foo; external 'MySharedLib' index 42;

and

Procedure foo; external 'MySharedLib' name 'foO';

where `foO' would be the external name as defined in the shared library.

My current idea now would be to define

Procedure foo; external; (* yields "Foo" *)

Var x: Integer; external; (* yields "X" *)

plus

Procedure foo; external name 'foO';

Var x: Integer; external name 'my_x';

to replace "AsmName 'foO'". Later we can extend this to allow a name of a shared library between `external' and `name'.

Once doing this, it could also be nice to make directives out of the other C-style storage qualifiers, too. I mean I'd like to replace

Var x: __static__ Integer; by x: Integer; static; y: __volatile__ Integer; by y: Integer; volatile;

etc.. My plan is to do it in a way that things like

Var static: Integer;

would still work.

I think it would *not* be a good idea to make

Procedure foO; external;

yield "foO", because (i) it would be difficult to implement and (ii) Pascal is a case-insensitive language, so everything outside string constants *must not* depend on casing at all.

Please tell me your opinion about this.

Yours,

Peter

e-mail: peter.gerwinski@uni-essen.de home address: D"usseldorfer Str. 35, 45145 Essen, Germany WWW: http://agnes.dida.physik.uni-essen.de/~peter