diff options
Diffstat (limited to 'libraries/base/GHC/Base.hs')
| -rw-r--r-- | libraries/base/GHC/Base.hs | 19 |
1 files changed, 13 insertions, 6 deletions
diff --git a/libraries/base/GHC/Base.hs b/libraries/base/GHC/Base.hs index 6f9d45469f..5f79b93773 100644 --- a/libraries/base/GHC/Base.hs +++ b/libraries/base/GHC/Base.hs @@ -904,16 +904,23 @@ augment g xs = g (:) xs -- Only activate this from phase 1, because that's -- when we disable the rule that expands (++) into foldr +"foldr/nil" forall k z. foldr k z [] = z +"foldr/single" forall k z x. foldr k z [x] = k x z +"foldr/short2" forall k z x1 x2. foldr k z [x1,x2] = k x1 (k x2 z) +"foldr/short3" forall k z x1 x2 x3. foldr k z [x1,x2,x3] = k x1 (k x2 (k x3 z)) +"foldr/short4" forall k z x1 x2 x3 x4. foldr k z [x1,x2,x3,x4] = k x1 (k x2 (k x3 (k x4 z))) + +-- "foldr/cons" forall k z x xs. foldr k z (x:xs) = k x (foldr k z xs) -- The foldr/cons rule looks nice, but it can give disastrously -- bloated code when commpiling -- array (a,b) [(1,2), (2,2), (3,2), ...very long list... ] -- i.e. when there are very very long literal lists --- So I've disabled it for now. We could have special cases --- for short lists, I suppose. --- "foldr/cons" forall k z x xs. foldr k z (x:xs) = k x (foldr k z xs) - -"foldr/single" forall k z x. foldr k z [x] = k x z -"foldr/nil" forall k z. foldr k z [] = z +-- So we disabled it, but have special cases for short lists up +-- to a completely arbitrary limit of 4. +-- +-- Note that static lists that are explicitly entered as such in the source, +-- the compiler desugars them to build (if they are short), and then normal +-- foldr/build rule fires, see note [Desugaring explicit lists] in DsExpr "foldr/cons/build" forall k z x (g::forall b. (a->b->b) -> b -> b) . foldr k z (x:build g) = k x (g k z) |