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  <TITLE>Using the Plain Erlang Back-end</TITLE>
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<A NAME="4"><!-- Empty --></A>
<H2>4 Using the Plain Erlang Back-end</H2>
<A NAME="4.1"><!-- Empty --></A>
<H3>4.1 Introduction</H3>

<P> The mapping of OMG IDL to the Erlang programming language when
Plain Erlang 
is the back-end of choice is similar to the one used in pure Erlang IDL
mapping. The only difference is on the generated code and the extended
use of pragmas for code generation: IDL functions are translated
to Erlang
module function calls.
<A NAME="4.2"><!-- Empty --></A>
<H3>4.2 Compiling the Code</H3>

<P> In the Erlang shell type :

<P> ic:gen(<CODE>&#60;filename&#62;, [{be, erl_plain}])</CODE>.<A NAME="4.3"><!-- Empty --></A>
<H3>4.3 Writing the Implementation File</H3>

<P> For each IDL interface <CODE>&#60;interface name&#62;</CODE> defined in the IDL file:

<P>
<UL>

<LI>
        Create the corresponding Erlang file that will hold the
        Erlang implementation of the IDL definitions. 

</LI>


<LI>
        Call the implementation file after the scope of the IDL interface, 
        followed by the suffix <CODE>_impl</CODE>.

</LI>


<LI>
        Export the implementation functions.

</LI>


</UL>

<P> For each function defined in the IDL interface :

<P>
<UL>

<LI>
        Implement an Erlang function that uses as arguments in the same
order, as the input ch_c_gen_serv_map.sgmlarguments described in the IDL file, and returns 
the value described in the interface.

</LI>


<LI>
        When using the function, follow the mapping described in chapter 2.

</LI>


</UL>
<A NAME="4.4"><!-- Empty --></A>
<H3>4.4 An Example</H3>

<P> <A NAME="plain_idl"><!-- Empty --></A>
        In this example, a file &#34;random.idl&#34; is generates code for the plain erlang
        back-end :

<P>
<UL>

<LI>
        Main file : &#34;plain.idl&#34;<BR>

        
<PRE>
           
module rmod {
 
  interface random {
 
    double produce();
 
    oneway void init(in long seed1, in long seed2, in long seed3);
 
  };
 
};

        
</PRE>


</LI>


</UL>

<P>Compile the file :
<PRE>
      Erlang (BEAM) emulator version 4.9
      
      Eshell V4.9  (abort with ^G)
      1&#62; ic:gen(random,[{be, erl_plain}]).
      Erlang IDL compiler version 2.5.1
      ok
      2&#62; 
    
</PRE>

<P>
<P> When the file &#34;random.idl&#34; is compiled it produces five files: two for 
the top scope, two for the interface scope, and one for the module
scope. The header files for top scope and interface
are empty and not shown here. In this case only the file for the interface 
<CODE>rmod_random.erl</CODE> is important :. 
<A NAME="generated files"><!-- Empty --></A>

<P>
<UL>

<LI>
        Erlang file for interface : &#34;rmod_random.erl&#34;<BR>

        
<PRE>

-module(rmod_random).
 
 
 
%% Interface functions
-export([produce/0, init/3]).
 
%%------------------------------------------------------------
%% Operation: produce
%% 
%%   Returns: RetVal
%%
produce() -&#62;
    rmod_random_impl:produce().
 
%%------------------------------------------------------------
%% Operation: init
%% 
%%   Returns: RetVal
%%
init(Seed1, Seed2, Seed3) -&#62;
    rmod_random_impl:init(Seed1, Seed2, Seed3).

        
</PRE>


</LI>


</UL>

<P>     The implementation file should be called <CODE>rmod_random_impl.erl</CODE> 
and could look like this:

<PRE>
      -module('rmod_random_impl').
      
      -export([produce/0,init/3]).
      
      
      produce()  -&#62;
        random:uniform().
       
      
      init(S1,S2,S3)  -&#62;
        random:seed(S1,S2,S3).
    
</PRE>

<P> Compiling the code : 
<PRE>
2&#62; make:all().
Recompile: rmod_random
Recompile: oe_random
Recompile: rmod_random_impl
up_to_date
      
</PRE>

<P>
<P> Running the example : 
<PRE>
3&#62;  rmod_random:init(1,2,3).
ok
4&#62;  rmod_random:produce().  
1.97963e-4
5&#62; 
      
</PRE>
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