[project @ 2003-06-25 08:20:20 by simonpj]

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

diff --git a/ghc/compiler/deSugar/DsListComp.lhs b/ghc/compiler/deSugar/DsListComp.lhs
index e9c455d..713d026 100644 (file)
--- a/ghc/compiler/deSugar/DsListComp.lhs
+++ b/ghc/compiler/deSugar/DsListComp.lhs
@@ -22,7 +22,7 @@ import CoreSyn
 import DsMonad         -- the monadery used in the desugarer
 import DsUtils
 
-import CmdLineOpts     ( opt_FoldrBuildOn )
+import CmdLineOpts     ( opt_IgnoreIfacePragmas, opt_RulesOff )
 import CoreUtils       ( exprType, mkIfThenElse )
 import Id              ( idType )
 import Var              ( Id )
@@ -51,11 +51,16 @@ dsListComp :: [TypecheckedStmt]
           -> DsM CoreExpr
 
 dsListComp quals elt_ty
-  |  not opt_FoldrBuildOn               -- Be boring
-  || isParallelComp quals
+  |  opt_RulesOff || opt_IgnoreIfacePragmas    -- 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
+  || isParallelComp quals                      -- Foldr-style desugaring can't handle
+                                               --   parallel list comprehensions
   = deListComp quals (mkNilExpr elt_ty)
 
-  | otherwise                           -- foldr/build lives!
+  | otherwise          -- Foldr/build should be enabled, so desugar 
+                       -- into foldrs and builds
   = newTyVarsDs [alphaTyVar]    `thenDs` \ [n_tyvar] ->
     let
        n_ty = mkTyVarTy n_tyvar