X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=docs%2Fcomm%2Fthe-beast%2Fmain.html;fp=docs%2Fcomm%2Fthe-beast%2Fmain.html;h=332ffaa501633aaed778f86b445f92080a4dad2f;hp=0000000000000000000000000000000000000000;hb=0065d5ab628975892cea1ec7303f968c3338cbe1;hpb=28a464a75e14cece5db40f2765a29348273ff2d2 diff --git a/docs/comm/the-beast/main.html b/docs/comm/the-beast/main.html new file mode 100644 index 0000000..332ffaa --- /dev/null +++ b/docs/comm/the-beast/main.html @@ -0,0 +1,35 @@ + + + + + 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. +

+ + +