Add the notion of "constructor-like" Ids for rule-matching

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

diff --git a/compiler/deSugar/DsListComp.lhs b/compiler/deSugar/DsListComp.lhs
index e5e1fd9..9508e51 100644 (file)
--- a/compiler/deSugar/DsListComp.lhs
+++ b/compiler/deSugar/DsListComp.lhs
@@ -15,8 +15,6 @@ Desugaring list comprehensions and array comprehensions
 
 module DsListComp ( dsListComp, dsPArrComp ) where
 
--- XXX This define is a bit of a hack, and should be done more nicely
-#define FAST_STRING_NOT_NEEDED 1
 #include "HsVersions.h"
 
 import {-# SOURCE #-} DsExpr ( dsLExpr, dsLocalBinds )
@@ -24,13 +22,14 @@ import {-# SOURCE #-} DsExpr ( dsLExpr, dsLocalBinds )
 import HsSyn
 import TcHsSyn
 import CoreSyn
+import MkCore
 
 import DsMonad         -- the monadery used in the desugarer
 import DsUtils
 
 import DynFlags
 import CoreUtils
-import Var
+import Id
 import Type
 import TysWiredIn
 import Match
@@ -57,7 +56,7 @@ dsListComp lquals body elt_ty = do
     dflags <- getDOptsDs
     let quals = map unLoc lquals
     
-    if not (dopt Opt_RewriteRules dflags) || dopt Opt_IgnoreInterfacePragmas dflags
+    if not (dopt Opt_EnableRewriteRules dflags) || dopt Opt_IgnoreInterfacePragmas dflags
        -- Either rules are switched off, or we are ignoring what there are;
        -- Either way foldr/build won't happen, so use the more efficient
        -- Wadler-style desugaring
@@ -511,10 +510,32 @@ dsPArrComp :: [Stmt Id]
             -> DsM CoreExpr
 dsPArrComp [ParStmt qss] body _  =  -- parallel comprehension
   dePArrParComp qss body
+
+-- Special case for simple generators:
+--
+--  <<[:e' | p <- e, qs:]>> = <<[: e' | qs :]>> p e
+--
+-- if matching again p cannot fail, or else
+--
+--  <<[:e' | p <- e, qs:]>> = 
+--    <<[:e' | qs:]>> p (filterP (\x -> case x of {p -> True; _ -> False}) e)
+--
+dsPArrComp (BindStmt p e _ _ : qs) body _ = do
+    filterP <- dsLookupGlobalId filterPName
+    ce <- dsLExpr e
+    let ety'ce  = parrElemType ce
+        false   = Var falseDataConId
+        true    = Var trueDataConId
+    v <- newSysLocalDs ety'ce
+    pred <- matchSimply (Var v) (StmtCtxt PArrComp) p true false
+    let gen | isIrrefutableHsPat p = ce
+            | otherwise            = mkApps (Var filterP) [Type ety'ce, mkLams [v] pred, ce]
+    dePArrComp qs body p gen
+
 dsPArrComp qs            body _  = do -- no ParStmt in `qs'
     sglP <- dsLookupGlobalId singletonPName
     let unitArray = mkApps (Var sglP) [Type unitTy, mkCoreTup []]
-    dePArrComp qs body (mkLHsPatTup []) unitArray
+    dePArrComp qs body (noLoc $ WildPat unitTy) unitArray
 
 
 
@@ -587,7 +608,7 @@ dePArrComp (LetStmt ds : qs) body pa cea = do
     v <- newSysLocalDs ty'cea
     clet <- dsLocalBinds ds (mkCoreTup (map Var xs))
     let'v <- newSysLocalDs (exprType clet)
-    let projBody = mkDsLet (NonRec let'v clet) $ 
+    let projBody = mkCoreLet (NonRec let'v clet) $ 
                    mkCoreTup [Var v, Var let'v]
         errTy    = exprType projBody
         errMsg   = "DsListComp.dePArrComp: internal error!"