<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Glue code</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REL="HOME" TITLE="The findlib User's Guide" HREF="index.html"><LINK REL="UP" TITLE="Complex packages" HREF="c274.html"><LINK REL="PREVIOUS" TITLE="Subpackages" HREF="x334.html"><LINK REL="NEXT" TITLE="How to create your own packages" HREF="c348.html"></HEAD ><BODY CLASS="SECT1" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >The findlib User's Guide</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="x334.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" >Chapter 5. Complex packages</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="c348.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="AEN341" >Glue code</A ></H1 ><P >Imagine we have two packages p and q that are normally independent, i.e. one can link p without q, and q without p. However, when both p and q are used in the same program, it is expected that they cooperate with each other. Of course, this situation can be modeled with the help of subpackages (a real-world example of this are p=lablgtk and q=lablgl).</P ><P >The idea is as follows: p has a subpackage p.for_q that contains code with special features for q, and q has a subpackage q.use_p that depends on p, p.for_q, and q, and that contains the code using the special features of p. Expressed in META files, p would define <PRE CLASS="PROGRAMLISTING" ># META file for p: requires = "..." archive = "..." package "for_q" ( requires = "p" archive = "..." )</PRE > and q would define <PRE CLASS="PROGRAMLISTING" ># META file for q: requires = "..." archive = "..." package "use_p" ( requires = "q,p.for_q" archive = "..." )</PRE > Of couse, the program using both libraries must explicitly enable the subpackages by mentioning "q.use_p" on the ocamlfind command line, otherwise the glue code would be omitted.</P ><P >Unfortunately, it is not possible to use the package predicates pkg_p and pkg_q to add archives depending on whether the other package is also selected. The problem is that the order cannot be specified, i.e. whether p must be linked first or q.</P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="x334.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="c348.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Subpackages</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="c274.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >How to create your own packages</TD ></TR ></TABLE ></DIV ></BODY ></HTML >