diff options
| -rw-r--r-- | libraries/base/Data/List.hs | 24 | ||||
| -rw-r--r-- | libraries/base/changelog.md | 2 |
2 files changed, 26 insertions, 0 deletions
diff --git a/libraries/base/Data/List.hs b/libraries/base/Data/List.hs index 193ebbc0c4..4f999261d8 100644 --- a/libraries/base/Data/List.hs +++ b/libraries/base/Data/List.hs @@ -106,6 +106,7 @@ module Data.List , isPrefixOf , isSuffixOf , isInfixOf + , isSubsequenceOf -- * Searching lists @@ -214,3 +215,26 @@ import Data.OldList hiding ( all, and, any, concat, concatMap, elem, find, foldl, foldl1, foldl', foldr, foldr1, mapAccumL, mapAccumR, maximum, maximumBy, minimum, minimumBy, length, notElem, null, or, product, sum ) + +import GHC.Base ( Bool(..), Eq((==)), otherwise ) + +-- | The 'isSubsequenceOf' function takes two lists and returns 'True' if the +-- first list is a subsequence of the second list. +-- +-- @'isSubsequenceOf' x y@ is equivalent to @'elem' x ('subsequences' y)@. +-- +-- /Since: 4.8.0.0/ +-- +-- ==== __Examples__ +-- +-- >>> isSubsequenceOf "GHC" "The Glorious Haskell Compiler" +-- True +-- >>> isSubsequenceOf ['a','d'..'z'] ['a'..'z'] +-- True +-- >>> isSubsequenceOf [1..10] [10,9..0] +-- False +isSubsequenceOf :: (Eq a) => [a] -> [a] -> Bool +isSubsequenceOf [] _ = True +isSubsequenceOf _ [] = False +isSubsequenceOf a@(x:a') (y:b) | x == y = isSubsequenceOf a' b + | otherwise = isSubsequenceOf a b diff --git a/libraries/base/changelog.md b/libraries/base/changelog.md index c3e1fa7240..86595d62e8 100644 --- a/libraries/base/changelog.md +++ b/libraries/base/changelog.md @@ -91,6 +91,8 @@ * Add `Alt`, an `Alternative` wrapper, to `Data.Monoid`. (#9759) + * Add `isSubsequenceOf` to `Data.List` (#9767) + ## 4.7.0.1 *Jul 2014* * Bundled with GHC 7.8.3 |