Comments only. Haddockify parts of TcRnTypes.

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

diff --git a/compiler/typecheck/FamInst.lhs b/compiler/typecheck/FamInst.lhs
index 224a960..5f4b2a3 100644 (file)
--- a/compiler/typecheck/FamInst.lhs
+++ b/compiler/typecheck/FamInst.lhs
@@ -1,19 +1,10 @@
 The @FamInst@ type: family instance heads
 
 \begin{code}
 The @FamInst@ type: family instance heads
 
 \begin{code}

-{-# OPTIONS -w #-}
--- The above warning supression flag is a temporary kludge.
--- While working on this module you are encouraged to remove it and fix
--- any warnings in the module. See
---     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
--- for details
-

 module FamInst ( 
         checkFamInstConsistency, tcExtendLocalFamInstEnv
     ) where
 
 module FamInst ( 
         checkFamInstConsistency, tcExtendLocalFamInstEnv
     ) where
 

-#include "HsVersions.h"
-

 import HscTypes
 import FamInstEnv
 import TcMType
 import HscTypes
 import FamInstEnv
 import TcMType

@@ -29,7 +20,7 @@ import LazyUniqFM
 import FiniteMap
 import FastString
 
 import FiniteMap
 import FastString
 

-import Maybe
+import Maybes

 import Monad
 \end{code}
 
 import Monad
 \end{code}
 

@@ -45,6 +36,16 @@ check whether the instances in the two modules are consistent, *unless* we can
 be certain that the instances of the two modules have already been checked for
 consistency during the compilation of modules that we import.
 
 be certain that the instances of the two modules have already been checked for
 consistency during the compilation of modules that we import.
 

+Why do we need to check?  Consider 
+   module X1 where               module X2 where
+    data T1                        data T2
+    type instance F T1 b = Int     type instance F a T2 = Char
+    f1 :: F T1 a -> Int                    f2 :: Char -> F a T2
+    f1 x = x                       f2 x = x
+
+Now if we import both X1 and X2 we could make (f2 . f1) :: Int -> Char.
+Notice that neither instance is an orphan.
+

 How do we know which pairs of modules have already been checked?  Any pair of
 modules where both modules occur in the `HscTypes.dep_finsts' set (of the
 `HscTypes.Dependencies') of one of our directly imported modules must have
 How do we know which pairs of modules have already been checked?  Any pair of
 modules where both modules occur in the `HscTypes.dep_finsts' set (of the
 `HscTypes.Dependencies') of one of our directly imported modules must have

@@ -116,8 +117,8 @@ checkFamInstConsistency famInstMods directlyImpMods
     -- already loaded in the EPS or they are in the HPT.
     --
     check modInstsEnv (ModulePair m1 m2)
     -- already loaded in the EPS or they are in the HPT.
     --
     check modInstsEnv (ModulePair m1 m2)

-      = let { instEnv1 = fromJust . lookupModuleEnv modInstsEnv $ m1
-           ; instEnv2 = fromJust . lookupModuleEnv modInstsEnv $ m2
+      = let { instEnv1 = (expectJust "checkFamInstConsistency") . lookupModuleEnv modInstsEnv $ m1
+           ; instEnv2 = (expectJust "checkFamInstConsistency") . lookupModuleEnv modInstsEnv $ m2

            ; insts1   = famInstEnvElts instEnv1
            }
         in
            ; insts1   = famInstEnvElts instEnv1
            }
         in

@@ -182,7 +183,7 @@ checkForConflicts inst_envs famInst
                         Nothing        -> panic "FamInst.checkForConflicts"
                         Just (tc, tys) -> tc `mkTyConApp` tys
              }
                         Nothing        -> panic "FamInst.checkForConflicts"
                         Just (tc, tys) -> tc `mkTyConApp` tys
              }

-       ; (tvs', _, tau') <- tcInstSkolType FamInstSkol ty
+       ; (_, _, tau') <- tcInstSkolType FamInstSkol ty

 
        ; let (fam, tys') = tcSplitTyConApp tau'
 
 
        ; let (fam, tys') = tcSplitTyConApp tau'
 

@@ -196,9 +197,9 @@ checkForConflicts inst_envs famInst
           conflictInstErr famInst (head conflicts)
        }
   where
           conflictInstErr famInst (head conflicts)
        }
   where

-      -- * In the case of data family instances, any overlap is fundamentally a 
+      -- - In the case of data family instances, any overlap is fundamentally a

       --   conflict (as these instances imply injective type mappings).
       --   conflict (as these instances imply injective type mappings).

-      -- * In the case of type family instances, overlap is admitted as long as 
+      -- - In the case of type family instances, overlap is admitted as long as

       --   the right-hand sides of the overlapping rules coincide under the
       --   overlap substitution.  We require that they are syntactically equal;
       --   anything else would be difficult to test for at this stage.
       --   the right-hand sides of the overlapping rules coincide under the
       --   overlap substitution.  We require that they are syntactically equal;
       --   anything else would be difficult to test for at this stage.

@@ -210,11 +211,13 @@ checkForConflicts inst_envs famInst
         rhs1   = substTy subst $ synTyConType tycon1
         rhs2   = substTy subst $ synTyConType tycon2
 
         rhs1   = substTy subst $ synTyConType tycon1
         rhs2   = substTy subst $ synTyConType tycon2
 

+conflictInstErr :: FamInst -> FamInst -> TcRn ()

 conflictInstErr famInst conflictingFamInst
   = addFamInstLoc famInst $
 conflictInstErr famInst conflictingFamInst
   = addFamInstLoc famInst $

-    addErr (hang (ptext SLIT("Conflicting family instance declarations:"))
+    addErr (hang (ptext (sLit "Conflicting family instance declarations:"))

               2 (pprFamInsts [famInst, conflictingFamInst]))
 
               2 (pprFamInsts [famInst, conflictingFamInst]))
 

+addFamInstLoc :: FamInst -> TcRn a -> TcRn a

 addFamInstLoc famInst thing_inside
   = setSrcSpan (mkSrcSpan loc loc) thing_inside
   where
 addFamInstLoc famInst thing_inside
   = setSrcSpan (mkSrcSpan loc loc) thing_inside
   where