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diff --git a/compiler/deSugar/DsExpr.lhs b/compiler/deSugar/DsExpr.lhs
index 11fddf5..d8bd7cd 100644 (file)
--- a/compiler/deSugar/DsExpr.lhs
+++ b/compiler/deSugar/DsExpr.lhs
@@ -656,6 +656,7 @@ dsExplicitList elt_ty xs
        ; let (dynamic_prefix, static_suffix) = spanTail is_static xs'
        ; if opt_SimpleListLiterals                     -- -fsimple-list-literals
          || not (dopt Opt_EnableRewriteRules dflags)   -- Rewrite rules off
+               -- Don't generate a build if there are no rules to eliminate it!
          || null dynamic_prefix   -- Avoid build (\c n. foldr c n xs)!
          then return $ mkListExpr elt_ty xs'
          else mkBuildExpr elt_ty (mkSplitExplicitList dynamic_prefix static_suffix) }