<li><a href="the-beast/ghci.html">GHCi</a>
<li><a href="the-beast/fexport.html">Implementation of
<code>foreign export</code></a>
+ <li><a href="the-beast/main.html">Compiling and running the Main module</code></a>
</ul>
<h2>RTS & Libraries</h2>
--- /dev/null
+<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
+<html>
+ <head>
+ <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1">
+ <title>The GHC Commentary - Compiling and running the Main module</title>
+ </head>
+
+ <body BGCOLOR="FFFFFF">
+ <h1>Compiling and running the Main module</h1>
+
+GHC allows you to determine which module contains the "main" function, and
+what that function is called, via the <code>-fmain-is</code> flag. The trouble is
+that the runtime system is fixed, so what symbol should it link to?
+<p>
+The current solution is this. Suppose the main function is <code>Foo.run</code>.
+<ul>
+<li>
+Then, when compiling module <code>Foo</code>, GHC adds an extra definition:
+<pre>
+ :Main.main = runIO Foo.run
+</pre>
+Now the RTS can invoke <code>:Main.main</code> to start the program. (This extra
+definition is inserted in TcRnDriver.checkMain.)
+<p><li>
+Before starting the program, though, the RTS also initialises the module tree
+by calling <code>init_:Main</code>, so when compiling the main module (Foo in this case),
+as well as generating <code>init_Foo</code> as usual, GHC also generates
+<pre>
+ init_zcMain() { init_Foo; }
+</pre>
+This extra initialisation code is generated in CodeGen.mkModuleInit.
+</ul>
+
+ </body>
+</html>
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