Here's the Haskell equivalent for anyone curious (Beware of curry[0]!):

    data Article = Article { title :: String
                           , author :: String
                           , tags :: [String]
                           } deriving (Show)
    
    articles = [ Article "Functional Java" "James Gosling" ["functional"]
               , Article "Practical java" "James Gosling" ["enterprise","architechture"]
               , Article "Imperative Haskell" "Simon P Jones" ["imperative", "purely imperative"] ]
    
    firstJavaArticle = headMay . filter (isInfixOf "Java" . title)
    
    allJavaArticles = filter (isInfixOf "Java" . title)
    
    groupArticlesByAuthor = groupBy ((==) `on` author)
    
    distinctArticleTags = nub . join . map tags

Full working code example with code imports and type signatures:

    import Data.List (isInfixOf, groupBy, nub)
    import Safe (headMay)
    import Data.Function (on)
    import Control.Monad (join)
    
    data Article = Article { title :: String
                           , author :: String
                           , tags :: [String]
                           } deriving (Show)
    
    articles :: [Article]
    articles = [ Article "Functional Java" "James Gosling" ["functional", "functional"]
               , Article "Practical java" "James Gosling" ["enterprise","architechture"]
               , Article "Imperative Haskell" "Simon P Jones" ["imperative", "purely imperative"] ]
    
    firstJavaArticle :: [Article] -> Maybe Article
    firstJavaArticle = headMay . filter (isInfixOf "Java" . title)
    
    -- implemented in terms using allJavaArticles (NOTE: This IS performant in Haskell and IIUC due to stream fusion will only iterate once. Did not verify though.)
    firstJavaArticle' :: [Article] -> Maybe Article
    firstJavaArticle' = headMay . allJavaArticles
    
    allJavaArticles :: [Article] -> [Article]
    allJavaArticles = filter (isInfixOf "Java" . title)
    
    groupArticlesByAuthor :: [Article] -> [[Article]]
    groupArticlesByAuthor = groupBy ((==) `on` author)
    
    distinctArticleTags :: [Article] -> [String]
    distinctArticleTags = nub . join . map tags
    
    main = undefined

0: http://en.wikipedia.org/wiki/Currying

http://tech.pro/tutorial/2011/functional-javascript-part-4-f....

https://www.haskell.org/haskellwiki/Currying