diff options
Diffstat (limited to 'libraries/base/Data/Foldable.hs')
| -rw-r--r-- | libraries/base/Data/Foldable.hs | 60 |
1 files changed, 60 insertions, 0 deletions
diff --git a/libraries/base/Data/Foldable.hs b/libraries/base/Data/Foldable.hs index a745f66092..1f20261943 100644 --- a/libraries/base/Data/Foldable.hs +++ b/libraries/base/Data/Foldable.hs @@ -282,6 +282,66 @@ instance Foldable Proxy where sum _ = 0 product _ = 1 +instance Foldable Dual where + foldMap = coerce + + elem = (. getDual) #. (==) + foldl = coerce + foldl' = coerce + foldl1 _ = getDual + foldr f z (Dual x) = f x z + foldr' = foldr + foldr1 _ = getDual + length _ = 1 + maximum = getDual + minimum = getDual + null _ = False + product = getDual + sum = getDual + toList (Dual x) = [x] + +instance Foldable Sum where + foldMap = coerce + + elem = (. getSum) #. (==) + foldl = coerce + foldl' = coerce + foldl1 _ = getSum + foldr f z (Sum x) = f x z + foldr' = foldr + foldr1 _ = getSum + length _ = 1 + maximum = getSum + minimum = getSum + null _ = False + product = getSum + sum = getSum + toList (Sum x) = [x] + +instance Foldable Product where + foldMap = coerce + + elem = (. getProduct) #. (==) + foldl = coerce + foldl' = coerce + foldl1 _ = getProduct + foldr f z (Product x) = f x z + foldr' = foldr + foldr1 _ = getProduct + length _ = 1 + maximum = getProduct + minimum = getProduct + null _ = False + product = getProduct + sum = getProduct + toList (Product x) = [x] + +instance Foldable First where + foldMap f = foldMap f . getFirst + +instance Foldable Last where + foldMap f = foldMap f . getLast + -- We don't export Max and Min because, as Edward Kmett pointed out to me, -- there are two reasonable ways to define them. One way is to use Maybe, as we -- do here; the other way is to impose a Bounded constraint on the Monoid |