diff options
Diffstat (limited to 'libraries/base/Data/Maybe.hs')
| -rw-r--r-- | libraries/base/Data/Maybe.hs | 15 |
1 files changed, 9 insertions, 6 deletions
diff --git a/libraries/base/Data/Maybe.hs b/libraries/base/Data/Maybe.hs index d8aad53b9e..d41ae92672 100644 --- a/libraries/base/Data/Maybe.hs +++ b/libraries/base/Data/Maybe.hs @@ -55,7 +55,7 @@ import GHC.Base -- >>> maybe False odd Nothing -- False -- --- Read an integer from a string using 'readMaybe'. If we succeed, +-- Read an integer from a string using 'Text.Read.readMaybe'. If we succeed, -- return twice the integer; that is, apply @(*2)@ to it. If instead -- we fail to parse an integer, return @0@ by default: -- @@ -65,7 +65,7 @@ import GHC.Base -- >>> maybe 0 (*2) (readMaybe "") -- 0 -- --- Apply 'show' to a @Maybe Int@. If we have @Just n@, we want to show +-- Apply 'Prelude.show' to a @Maybe Int@. If we have @Just n@, we want to show -- the underlying 'Int' @n@. But if we have 'Nothing', we return the -- empty string instead of (for example) \"Nothing\": -- @@ -161,7 +161,7 @@ fromJust (Just x) = x -- >>> fromMaybe "" Nothing -- "" -- --- Read an integer from a string using 'readMaybe'. If we fail to +-- Read an integer from a string using 'Text.Read.readMaybe'. If we fail to -- parse an integer, we want to return @0@ by default: -- -- >>> import Text.Read ( readMaybe ) @@ -228,9 +228,12 @@ maybeToList (Just x) = [x] -- >>> maybeToList $ listToMaybe [1,2,3] -- [1] -- -listToMaybe :: [a] -> Maybe a -listToMaybe [] = Nothing -listToMaybe (a:_) = Just a +listToMaybe :: [a] -> Maybe a +listToMaybe = foldr (const . Just) Nothing +{-# INLINE listToMaybe #-} +-- We define listToMaybe using foldr so that it can fuse via the foldr/build +-- rule. See #14387 + -- | The 'catMaybes' function takes a list of 'Maybe's and returns -- a list of all the 'Just' values. |