<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Appending to variables</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="Defining additional predicates" HREF="x307.html"><LINK REL="NEXT" TITLE="Subpackages" HREF="x334.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="x307.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="x334.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="AEN322" >Appending to variables</A ></H1 ><P >The syntax <PRE CLASS="PROGRAMLISTING" >varname ( predname1, predname2, ... ) += "value"</PRE > (note the "+=" operator) can be used to append values to variables depending on whether predicates are true. The "+=" lines in the META file are evaluated one after the other, and <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >every</I ></SPAN > line is selected for which the formal predicates are satisfied, and these lines are added to the current value of the variable. This is different from the "=" operator where only the most specific assignment is taken.</P ><P >The values are considered as space-separated words when they are appended, i.e. the new words are added to the list of current words.</P ><P >For example, in the hypothetic META file <PRE CLASS="PROGRAMLISTING" >var(p) += "a" var(p,q) += "b"</PRE > the value of var is "a b" if both p and q are true, and the value is only "a" is only p is true (and the value is empty otherwise). If the operator "=" had been used, the value would have been only "b" when both p and q are true.</P ><P >In the case that there both "=" and "+=" settings for the same variable, a special algorithm is used: First the most specific "=" setting is determined, and second all matching "+=" settings are appended in the order they appear in the file.</P ><P >Finally, here is a real-world example. Imagine you have an archive p.cma and a special extension for the toploop, p_top.cma. Furthermore, there is a special debugging version p_dev.cma that replaces p.cma during development. You can now simply write <PRE CLASS="PROGRAMLISTING" >archive(byte) = "p.cma" archive(byte,development) = "p_dev.cma" archive(byte,toploop) += "p_top.cma"</PRE > to select <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >either</I ></SPAN > p.cma or p_dev.cma, and append p_top.cma for toploops to whatever was selected in the first step.</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="x307.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="x334.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Defining additional predicates</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="c274.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Subpackages</TD ></TR ></TABLE ></DIV ></BODY ></HTML >