[Caml-list] Reference to undefined global using Dynlink module.

[Caml-list] Reference to undefined global using Dynlink module.

[Dmitri Boulytchev]

        Hello everybody,

        I didn't get as answer browsing the archive so I decided to ask.
        
        How to avoid "Reference to undefined global ***" error during
        loading *.cmo via Dynlink  module?

        To be more precise: the loading foo.cmo uses Num module. All
        interfaces (including "Num") are added in the client program. On
        loading I get an error "Reference to undefined global Num".

        Why am I wrong and whether am I wrong at all? :))

        Best regards,
        Dmitri Boulytchev,
        St.Petersburg State University.
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Re: [Caml-list] Reference to undefined global using Dynlink module.

[Alessandro Baretta]

Dmitri Boulytchev wrote:
>         Hello everybody,
> 
>         I didn't get as answer browsing the archive so I decided to ask.
>         
>         How to avoid "Reference to undefined global ***" error during
>         loading *.cmo via Dynlink  module?

I had the same problem so I am competent on the subject. I 
bet your code looks like the following:

a.ml
***********
open Dynlink

let foo = <whatever>

...
let _ = loadfile "b.cmo"

b.ml
***********


... A.foo ...

      ^
      |
      |
Thi is your problem. When you try to access A.foo, module A 
has not completed initialization, so it's values appear to 
be yet undefined to all other modules.

What you have to do is create a main.ml file which is 
initialized last--that is, linked last--where you call the 
Dynlink library to load b.ml. Here's how to do it:

a.ml
***************
let foo = <whatever>


b.ml
***************
... A.foo ....


main.ml
***************
open Dynlink

let _ = loadfile "b.cmo"


Makefile
*******************
all : dynlinked_prog b.cmo

b.cmo : b.ml
	ocamlc -c b.ml

dynlinked_prog: a.ml main.ml
	ocamlc -o $@ a.ml main.ml
# notice the order in which the files are compiled

*******************

When you run make you get an executable and a CMO. When you 
run the executable, all the modules that are statically 
linked into it are initialized in the order they were 
specified in. So first A is initialized (and A.foo is 
defined); then, main is initialized (and Dynlink.loadfile is 
called). Thus, when loadfile is called, no dynamic linking 
error occurs.

Alex


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