[project @ 2003-02-04 12:33:05 by simonpj]

[ghc-hetmet.git] / ghc / compiler / typecheck / TcRnTypes.lhs

diff --git a/ghc/compiler/typecheck/TcRnTypes.lhs b/ghc/compiler/typecheck/TcRnTypes.lhs
index d7bfd17..a42cbc8 100644 (file)
--- a/ghc/compiler/typecheck/TcRnTypes.lhs
+++ b/ghc/compiler/typecheck/TcRnTypes.lhs
@@ -235,6 +235,7 @@ data TopEnv -- Built once at top level then does not change
                -- PIT, ImportedModuleInfo
                -- DeclsMap, IfaceRules, IfaceInsts, InstGates
                -- TypeEnv, InstEnv, RuleBase
+               -- Mutable, because we demand-load declarations that extend the state
 
        top_hpt  :: HomePackageTable,
                -- The home package table that we've accumulated while 
@@ -273,15 +274,15 @@ data TcGblEnv
                -- (Ids defined in this module start in the local envt, 
                --  though they move to the global envt during zonking)
        
-               -- Cached things
-       tcg_ist :: Name -> Maybe TyThing,       -- Imported symbol table
-               -- Global type env: a combination of tcg_eps, tcg_hpt
-               --      (but *not* tcg_type_env; no deep reason)
-               -- When the PCS changes this must be refreshed, 
-               -- notably after running some compile-time code
-       
-       tcg_inst_env :: InstEnv,        -- Global instance env: a combination of 
+       tcg_inst_env :: TcRef InstEnv,  -- Global instance env: a combination of 
                                        --      tc_pcs, tc_hpt, *and* tc_insts
+               -- This field is mutable so that it can be updated inside a
+               -- Template Haskell splice, which might suck in some new
+               -- instance declarations.  This is a slightly differen strategy
+               -- than for the type envt, where we look up first in tcg_type_env
+               -- and then in the mutable EPS, because the InstEnv for this module
+               -- is constructed (in principle at least) only from the modules
+               -- 'below' this one, so it's this-module-specific
 
                -- Now a bunch of things about this module that are simply 
                -- accumulated, but never consulted until the end.  
@@ -667,13 +668,19 @@ data Inst
        TcThetaType     -- The (types of the) dictionaries to which the function
                        -- must be applied to get the method
 
-       TcTauType       -- The type of the method
+       TcTauType       -- The tau-type of the method
 
        InstLoc
 
-       -- INVARIANT: in (Method u f tys theta tau loc)
+       -- INVARIANT 1: in (Method u f tys theta tau loc)
        --      type of (f tys dicts(from theta)) = tau
 
+       -- INVARIANT 2: tau must not be of form (Pred -> Tau)
+       --   Reason: two methods are considerd equal if the 
+       --           base Id matches, and the instantiating types
+       --           match.  The TcThetaType should then match too.
+       --   This only bites in the call to tcInstClassOp in TcClassDcl.mkMethodBind
+
   | LitInst
        Id
        HsOverLit       -- The literal from the occurrence site