FIX #1759 while respecting the ticks

[ghc-hetmet.git] / compiler / deSugar / DsGRHSs.lhs

diff --git a/compiler/deSugar/DsGRHSs.lhs b/compiler/deSugar/DsGRHSs.lhs
index eea61ba..4daab97 100644 (file)
--- a/compiler/deSugar/DsGRHSs.lhs
+++ b/compiler/deSugar/DsGRHSs.lhs
@@ -1,9 +1,18 @@
 %
+% (c) The University of Glasgow 2006
 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
 %
-\section[DsGRHSs]{Matching guarded right-hand-sides (GRHSs)}
+
+Matching guarded right-hand-sides (GRHSs)
 
 \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 DsGRHSs ( dsGuarded, dsGRHSs ) where
 
 #include "HsVersions.h"
@@ -11,20 +20,19 @@ module DsGRHSs ( dsGuarded, dsGRHSs ) where
 import {-# SOURCE #-} DsExpr  ( dsLExpr, dsLocalBinds )
 import {-# SOURCE #-} Match   ( matchSinglePat )
 
-import HsSyn           ( Stmt(..), HsExpr(..), GRHSs(..), GRHS(..), 
-                         LHsExpr, HsMatchContext(..), Pat(..) )
-import CoreSyn         ( CoreExpr )
-import Var             ( Id )
-import Type            ( Type )
+import HsSyn
+import CoreSyn
+import Var
+import Type
 
 import DsMonad
 import DsUtils
-import Unique          ( Uniquable(..) )
-import PrelInfo                ( nON_EXHAUSTIVE_GUARDS_ERROR_ID )
-import TysWiredIn      ( trueDataConId )
-import PrelNames       ( otherwiseIdKey, hasKey )
-import Name            ( Name )
-import SrcLoc          ( unLoc, Located(..) )
+import PrelInfo
+import TysWiredIn
+import PrelNames
+import Name
+import SrcLoc
+
 \end{code}
 
 @dsGuarded@ is used for both @case@ expressions and pattern bindings.
@@ -54,14 +62,15 @@ dsGRHSs :: HsMatchContext Name -> [Pat Id]  -- These are to build a MatchContext
        -> GRHSs Id                             -- Guarded RHSs
        -> Type                                 -- Type of RHS
        -> DsM MatchResult
-
-dsGRHSs hs_ctx pats (GRHSs grhss binds) rhs_ty
-  = mappM (dsGRHS hs_ctx pats rhs_ty) grhss    `thenDs` \ match_results ->
+dsGRHSs hs_ctx pats grhssa@(GRHSs grhss binds) rhs_ty = do
+    match_results <- mappM (dsGRHS hs_ctx pats rhs_ty) grhss
     let 
        match_result1 = foldr1 combineMatchResults match_results
-       match_result2 = adjustMatchResultDs (dsLocalBinds binds) match_result1
+       match_result2 = adjustMatchResultDs 
+                                 (\e -> dsLocalBinds binds e) 
+                                 match_result1
                -- NB: nested dsLet inside matchResult
-    in
+    --
     returnDs match_result2
 
 dsGRHS hs_ctx pats rhs_ty (L loc (GRHS guards rhs))
@@ -94,14 +103,12 @@ matchGuards [] ctx rhs rhs_ty
        -- you don't get a "non-exhaustive eqns" message when the guards 
        -- finish in "otherwise".
        -- NB:  The success of this clause depends on the typechecker not
-       --      wrapping the 'otherwise' in empty HsTyApp or HsCoerce constructors
+       --      wrapping the 'otherwise' in empty HsTyApp or HsWrap constructors
        --      If it does, you'll get bogus overlap warnings
-matchGuards (ExprStmt (L _ (HsVar v)) _ _ : stmts) ctx rhs rhs_ty
-  |  v `hasKey` otherwiseIdKey
-  || v `hasKey` getUnique trueDataConId        
-       -- trueDataConId doesn't have the same unique as trueDataCon
-  = matchGuards stmts ctx rhs rhs_ty
-
+matchGuards (ExprStmt e _ _ : stmts) ctx rhs rhs_ty
+  | Just addTicks <- isTrueLHsExpr e
+  = matchGuards stmts ctx rhs rhs_ty   `thenDs` \ match_result ->
+    returnDs (adjustMatchResultDs addTicks match_result)
 matchGuards (ExprStmt expr _ _ : stmts) ctx rhs rhs_ty
   = matchGuards stmts ctx rhs rhs_ty   `thenDs` \ match_result ->
     dsLExpr expr                       `thenDs` \ pred_expr ->
@@ -119,6 +126,31 @@ matchGuards (BindStmt pat bind_rhs _ _ : stmts) ctx rhs rhs_ty
   = matchGuards stmts ctx rhs rhs_ty   `thenDs` \ match_result ->
     dsLExpr bind_rhs                   `thenDs` \ core_rhs ->
     matchSinglePat core_rhs ctx pat rhs_ty match_result
+
+isTrueLHsExpr :: LHsExpr Id -> Maybe (CoreExpr -> DsM CoreExpr)
+
+-- Returns Just {..} if we're sure that the expression is True
+-- I.e.   * 'True' datacon
+--       * 'otherwise' Id
+--       * Trivial wappings of these
+-- The arguments to Just are any HsTicks that we have found,
+-- because we still want to tick then, even it they are aways evaluted.
+isTrueLHsExpr (L _ (HsVar v)) |  v `hasKey` otherwiseIdKey
+                             || v `hasKey` getUnique trueDataConId     
+                                      = Just returnDs
+       -- trueDataConId doesn't have the same unique as trueDataCon
+isTrueLHsExpr (L loc (HsTick    ix frees e)) 
+    | Just ticks <- isTrueLHsExpr e   = Just (\ e1 -> 
+                            ticks e1 `thenDs` \ e2 -> 
+                            mkTickBox ix frees e2)
+   -- This encodes that the result is constant True for Hpc tick purposes;
+   -- which is specifically what isTrueLHsExpr is trying to find out.
+isTrueLHsExpr (L loc (HsBinTick ixT _ e))
+    | Just ticks <- isTrueLHsExpr e   = Just (\ e1 -> 
+                            ticks e1 `thenDs` \ e2 -> 
+                            mkTickBox ixT [] e2)
+isTrueLHsExpr (L _ (HsPar e))         = isTrueLHsExpr e
+isTrueLHsExpr other = Nothing
 \end{code}
 
 Should {\em fail} if @e@ returns @D@