[[project @ 2003-10-29 19:05:55 by simonpj] simonpj**20031029190556 Add info about compiling the Main module ] { addfile ./ghc/docs/comm/the-beast/main.html hunk ./ghc/docs/comm/index.html 77 +

Compiling and running the Main module hunk ./ghc/docs/comm/the-beast/main.html 1 + + + + + The GHC Commentary - Compiling and running the Main module + + + +

Compiling and running the Main module

+ +GHC allows you to determine which module contains the "main" function, and +what that function is called, via the -fmain-is flag. The trouble is +that the runtime system is fixed, so what symbol should it link to? +

+The current solution is this. Suppose the main function is Foo.run. +

+Then, when compiling module Foo, GHC adds an extra definition: +
```
+  :Main.main = runIO Foo.run
+
```
+Now the RTS can invoke :Main.main to start the program. (This extra +definition is inserted in TcRnDriver.checkMain.) +
+Before starting the program, though, the RTS also initialises the module tree +by calling init_:Main, so when compiling the main module (Foo in this case), +as well as generating init_Foo as usual, GHC also generates +
```
+  init_zcMain() { init_Foo; }
+
```
+This extra initialisation code is generated in CodeGen.mkModuleInit. +

+ + + }