[Haskell-cafe] FW: GHC.Prim.realWorld

[Simon Peyton-Jones]

|   I'd like to know what the function GHC.Prim.realWorld does exactlly
| in the STG code below:

Think of it as a fixed value.  We want the join point $w$j to be a
function, with at least one argument, otherwise it'll be evaluated
eagerly (since it has a primitive type), which is semantically wrong.
It's rather like saying (\().e), only cheaper, because passing ()
requires you to actually pass a value, whereas the 'realword' token has
a type that says "you don't need to pass anything at runtime".

GHC.Prim is a built-in module for functions and types that can't be
defined in Haskell.

The functions in GHC.Prim are enumerated in
ghc/compiler/prelude/primops.txt.pp

Simon

| 
| PrelBase.divInt# =
|     \r [x# y#]
| 	let-no-escape {
| 	  $w$j =
| 	      sat-only \r [w]
| 		  case <# [x# 0] of wild {
| 		    GHC.Base.False -> quotInt# [x# y#];
| 		    GHC.Base.True ->
| 			case ># [y# 0] of wild1 {
| 			  GHC.Base.True ->
| 			      case +# [x# 1] of sat_s10t {
| 				__DEFAULT ->
| 				    case quotInt# [sat_s10t y#] of
sat_s10w {
| 				      __DEFAULT -> -# [sat_s10w 1];
| 				    };
| 			      };
| 			  GHC.Base.False -> quotInt# [x# y#];
| 			};
| 		  };
| 	} in
| 	  case ># [x# 0] of wild {
| 	    GHC.Base.False -> $w$j GHC.Prim.realWorld#;
| 	    GHC.Base.True ->
| 		case <# [y# 0] of wild1 {
| 		  GHC.Base.True ->
| 		      case -# [x# 1] of sat_s10I {
| 			__DEFAULT ->
| 			    case quotInt# [sat_s10I y#] of sat_s10L {
| 			      __DEFAULT -> -# [sat_s10L 1];
| 			    };
| 		      };
| 		  GHC.Base.False -> $w$j GHC.Prim.realWorld#;
| 		};
| 	  };
| 
|   Finally, where is the module GHC.Prim defined ?  I've looked for it
| in GHC source directories but I haven't found it.  Is it part of the
| runtime system ?
| 
| Thanks in advance,
| 
| --
| ________________________________
| Monique Louise B.Monteiro
| Msc Student in Computer Science
| Center of Informatics
| Federal University of Pernambuco