X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Fiface%2FLoadIface.lhs;h=1ebbd39b75b6c389df3b0941a81507eee71455e2;hb=ead3abe7fbf33f019549a05ad9dd3cd22ef3adab;hp=8ca7b41ac5dd23d41c4f137f7078d2ca18047562;hpb=686d87447e2186e2aa55e1a925f0a3a8e94872f5;p=ghc-hetmet.git

diff --git a/compiler/iface/LoadIface.lhs b/compiler/iface/LoadIface.lhs
index 8ca7b41..1ebbd39 100644
--- a/compiler/iface/LoadIface.lhs
+++ b/compiler/iface/LoadIface.lhs
@@ -118,6 +118,7 @@ loadInterfaceForName doc name
 
 -- | An 'IfM' function to load the home interface for a wired-in thing,
 -- so that we're sure that we see its instance declarations and rules
+-- See Note [Loading instances]
 loadWiredInHomeIface :: Name -> IfM lcl ()
 loadWiredInHomeIface name
   = ASSERT( isWiredInName name )
@@ -134,6 +135,27 @@ loadSysInterface doc mod_name
 	    Succeeded iface -> return iface }
 \end{code}
 
+Note [Loading instances]
+~~~~~~~~~~~~~~~~~~~~~~~~
+We need to make sure that we have at least *read* the interface files
+for any module with an instance decl or RULE that we might want.  
+
+* If the instance decl is an orphan, we have a whole separate mechanism
+  (loadOprhanModules)
+
+* If the instance decl not an orphan, then the act of looking at the
+  TyCon or Class will force in the defining module for the
+  TyCon/Class, and hence the instance decl
+
+* BUT, if the TyCon is a wired-in TyCon, we don't really need its interface;
+  but we must make sure we read its interface in case it has instances or
+  rules.  That is what LoadIface.loadWiredInHomeInterface does.  It's called
+  from TcIface.{tcImportDecl, checkWiredInTyCon, ifCHeckWiredInThing}
+
+All of this is done by the type checker. The renamer plays no role.
+(It used to, but no longer.)
+
+
 
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