Missing something in getting C and Ocaml to Work Together

Missing something in getting C and Ocaml to Work Together

[Steve Stevenson]

Good Afternoon,

	I have a very simple application. I have the main in ocaml and 
the rest of the system in C. I'm just trying something very straight
forward.


external cmainarg : int -> string array -> unit = "cmainarg"
external io_infile_stdin : unit -> unit = "io_infile_stdin"
external cmaininit : unit -> unit = "cmaininit"


let main() =
  cmainarg  (Array.length Sys.argv)  Sys.argv;
  io_infile_stdin ();
  cmaininit();
  0
(*end*)

And I use this to compile

ocamlc main.cmo -custom -cclib csrc/libmainc.a

When I do, I get no errors but 

ocamlrun a.out

produces

Fatal error: this bytecode file cannot run on this bytecode interpreter
Mismatch on primitive `cmainarg'

What am I doing wrong?

Thanks. (NO, I don't know who will be president yet. :-)

steve

Re: Missing something in getting C and Ocaml to Work Together

[Wolfgang Lux]

Steve Stevenson wrote

> And I use this to compile
> 
> ocamlc main.cmo -custom -cclib csrc/libmainc.a
> 
> When I do, I get no errors but 
> 
> ocamlrun a.out
> 
> produces
> 
> Fatal error: this bytecode file cannot run on this bytecode interpreter
> Mismatch on primitive `cmainarg'
> 
> What am I doing wrong?

You use the standard bytecode interpreter, which does not know anything 
about your C function, to start your custom executable. Just use

 ./a.out

to start the program. Actually, you (nearly) never have to call ocamlrun 
yourself, the bytecode program contains some nice magic to start up the 
right bytecode interpreter for you.

Regards
Wolfgang

--
Wolfgang Lux				  Phone: +49-251-83-38263
Institut fuer Wirtschaftinformatik	    FAX: +49-251-83-38259
Universitaet Muenster		      Email: wlux@uni-muenster.de

Re: Missing something in getting C and Ocaml to Work Together

[Xavier Leroy]

> 	I have a very simple application. I have the main in ocaml and 
> the rest of the system in C. I'm just trying something very straight
> forward.
> [...]
> ocamlc main.cmo -custom -cclib csrc/libmainc.a
> When I do, I get no errors but 
> ocamlrun a.out
> produces
> Fatal error: this bytecode file cannot run on this bytecode interpreter
> Mismatch on primitive `cmainarg'

Just run a.out directly, as in "./a.out".  The -custom flag to ocamlc
causes it to produce a "mixed" executable containing both OCaml
bytecode and a specially tailored bytecode interpreter that includes
your C code.

Using the standard "ocamlrun" bytecode interpreter on such an
executable fails, because ocamlrun doesn't contain the C functions that
the bytecode part of the mixed executable calls ("cmainarg" here).

Hope this helps,

- Xavier Leroy

Re: Missing something in getting C and Ocaml to Work Together

[Sven LUTHER]

On Wed, Nov 22, 2000 at 09:29:17PM +0100, Xavier Leroy wrote:
> > 	I have a very simple application. I have the main in ocaml and 
> > the rest of the system in C. I'm just trying something very straight
> > forward.
> > [...]
> > ocamlc main.cmo -custom -cclib csrc/libmainc.a
> > When I do, I get no errors but 
> > ocamlrun a.out
> > produces
> > Fatal error: this bytecode file cannot run on this bytecode interpreter
> > Mismatch on primitive `cmainarg'
> 
> Just run a.out directly, as in "./a.out".  The -custom flag to ocamlc
> causes it to produce a "mixed" executable containing both OCaml
> bytecode and a specially tailored bytecode interpreter that includes
> your C code.
> 
> Using the standard "ocamlrun" bytecode interpreter on such an
> executable fails, because ocamlrun doesn't contain the C functions that
> the bytecode part of the mixed executable calls ("cmainarg" here).

Any news on arch independent cutsom code you spoke about some time ago ?

Friendly,

Sven Luther

Typing the result of a function

[Mattias Waldau]

I know how to type the arguments, and I like to do it, since I will get the
compile errors directly, not first when I use the function.

Thus, I typical write a function like

(* return the column called name *)
let find (columns:columns) (name:column_type) =
  List.find ( fun column -> column.data_type = name ) columns.columns

which has typing

val find : columns -> column_type -> column = <fun>

If I use the interactive environment, I see that I get the expected result
column. I needed to see this, since this is my first use of List.find, and I
wanted to be sure that it returned the column.

However, I would have liked to say this already in the definition of find,
that the result of my function find should be a column. How is this done?

/mattias

P.s. I like to type, since I think it is belongs to the documentation of the
code.

P.P.s. How to type arguments is not very well described in the
documentation. I found one example, twice.

Re: Typing the result of a function

[Pierre Weis]

> I know how to type the arguments, and I like to do it, since I will get the
> compile errors directly, not first when I use the function.
> 
> Thus, I typical write a function like
> 
> (* return the column called name *)
> let find (columns:columns) (name:column_type) =
>   List.find ( fun column -> column.data_type = name ) columns.columns
> 
> which has typing
> 
> val find : columns -> column_type -> column = <fun>
> 
> If I use the interactive environment, I see that I get the expected result
> column. I needed to see this, since this is my first use of List.find, and I
> wanted to be sure that it returned the column.
> 
> However, I would have liked to say this already in the definition of find,
> that the result of my function find should be a column. How is this done?
>
> /mattias
> 
> P.s. I like to type, since I think it is belongs to the documentation of the
> code.

I would suggest to let those types in the module interfaces where
you should already have written the documentation of the code then ...

> P.P.s. How to type arguments is not very well described in the
> documentation. I found one example, twice.

Type constraints are simply introduced by a : symbol and should
normally be enclosed into parens (as in your code above). However, you
can use a simpler form to constraint the results of functions, just
write the constraints before the = sign:

let find (columns:columns) (name:column_type) : column =
   List.find ( fun column -> column.data_type = name ) columns.columns

Hope this helps,

Pierre Weis

INRIA, Projet Cristal, Pierre.Weis@inria.fr, http://cristal.inria.fr/~weis/