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<!DOCTYPE chapter SYSTEM "chapter.dtd">

<chapter>
  <header>
    <copyright>
      <year>1998</year><year>2016</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at
 
          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.
    
    </legalnotice>

    <title>Using the Plain Erlang Back-end</title>
    <prepared></prepared>
    <docno></docno>
    <date>98-05-06</date>
    <rev>B</rev>
    <file>ch_erl_plain.xml</file>
  </header>

  <section>
    <title>Introduction</title>
    <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.</p>
  </section>

  <section>
    <title>Compiling the Code</title>
    <p>In the Erlang shell type :</p>
    <p>ic:gen(<c><![CDATA[<filename>, [{be, erl_plain}])]]></c>.</p>
  </section>

  <section>
    <title>Writing the Implementation File</title>
    <p>For each IDL interface <c><![CDATA[<interface name>]]></c> defined in the IDL file:</p>
    <list type="bulleted">
      <item>Create the corresponding Erlang file that will hold the
       Erlang implementation of the IDL definitions.  </item>
      <item>Call the implementation file after the scope of the IDL interface, 
       followed by the suffix <c>_impl</c>.</item>
      <item>Export the implementation functions.</item>
    </list>
    <p>For each function defined in the IDL interface :</p>
    <list type="bulleted">
      <item>Implement an Erlang function that uses as arguments in the same
       order, as the input arguments described in the IDL file, and returns 
       the value described in the interface.</item>
      <item>When using the function, follow the mapping described in chapter 2.</item>
    </list>
  </section>

  <section>
    <title>An Example</title>
    <p>      <marker id="plain_idl"></marker>

      In this example, a file "random.idl" is generates code for the plain Erlang
      back-end :</p>
    <list type="bulleted">
      <item>
        <p>Main file : "plain.idl"</p>
        <code type="none">

module rmod {
 
  interface random {
 
    double produce();
 
    oneway void init(in long seed1, in long seed2, in long seed3);
 
  };
 
};
        </code>
      </item>
    </list>
    <p>Compile the file :</p>
    <code type="none">
      Erlang (BEAM) emulator version 4.9
      
      Eshell V4.9  (abort with ^G)
      1> ic:gen(random,[{be, erl_plain}]).
      Erlang IDL compiler version 2.5.1
      ok
      2> 
    </code>
    <p></p>
    <p>When the file "random.idl" 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 
      <c>rmod_random.erl</c> is important :. 
            <marker id="generated files"></marker>
</p>
    <list type="bulleted">
      <item>
        <p>Erlang file for interface : "rmod_random.erl"</p>
        <code type="none">

-module(rmod_random).
 
 
 
%% Interface functions
-export([produce/0, init/3]).
 
%%------------------------------------------------------------
%% Operation: produce
%% 
%%   Returns: RetVal
%%
produce() ->
    rmod_random_impl:produce().
 
%%------------------------------------------------------------
%% Operation: init
%% 
%%   Returns: RetVal
%%
init(Seed1, Seed2, Seed3) ->
    rmod_random_impl:init(Seed1, Seed2, Seed3).
        </code>
      </item>
    </list>
    <p>The implementation file should be called <c>rmod_random_impl.erl</c> 
      and could look like this:</p>
    <code type="none">
      -module('rmod_random_impl').
      
      -export([produce/0,init/3]).
      
      
      produce()  ->
        random:uniform().
       
      
      init(S1,S2,S3)  ->
        random:seed(S1,S2,S3).
    </code>
    <p>Compiling the code : </p>
    <code type="none">
2> make:all().
Recompile: rmod_random
Recompile: oe_random
Recompile: rmod_random_impl
up_to_date
    </code>
    <p></p>
    <p>Running the example : </p>
    <code type="none">
3>  rmod_random:init(1,2,3).
ok
4>  rmod_random:produce().  
1.97963e-4
5> 
    </code>
  </section>
</chapter>

