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diff --git a/docs/comm/the-beast/main.html b/docs/comm/the-beast/main.html new file mode 100644 index 0000000000..332ffaa501 --- /dev/null +++ b/docs/comm/the-beast/main.html @@ -0,0 +1,35 @@ +<!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> |