HXT/Practical/Simple2

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Revision as of 01:05, 5 August 2007 by Mrd (talk | contribs) (simple2 -- more involved example)

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{-# OPTIONS -farrows -fno-monomorphism-restriction #-} import Text.XML.HXT.Arrow -- This example demonstrates a more complex XML parse, -- involving multiple levels, attributes, inner lists, -- and dealing with optional data. -- Example data drawn from: -- http://www.ibiblio.org/xml/books/bible/examples/05/5-1.xml -- save as: simple2.xml data Team = Team { teamName, division, league, city :: String, players :: [Player] } deriving (Show, Eq) data Player = Player { firstName, lastName, position :: String, atBats, hits :: Maybe Int, era :: Maybe Float } deriving (Show, Eq) parseXML file = readDocument [(a_validate,v_0)] file atTag tag = deep (isElem >>> hasName tag) -- Incremental development of the getTeams function: -- First, list the teams. -- Try it out in GHCi: -- Main> runX (parseXML "simple2.xml" >>> getTeams1) getTeams1 = atTag "LEAGUE" >>> proc l -> do leagName <- getAttrValue "NAME" -< l divi <- atTag "DIVISION" -< l diviName <- getAttrValue "NAME" -< divi team <- atTag "TEAM" -< divi teamName <- getAttrValue "NAME" -< team returnA -< (leagName, diviName, teamName) -- getTeams2 also lists the players. -- But there is a catch; now teams without players -- are being left out. (This behavior is familiar to -- users of the List monad) getTeams2 = atTag "LEAGUE" >>> proc l -> do leagName <- getAttrValue "NAME" -< l divi <- atTag "DIVISION" -< l diviName <- getAttrValue "NAME" -< divi team <- atTag "TEAM" -< divi teamName <- getAttrValue "NAME" -< team player <- atTag "PLAYER" -< team fName <- getAttrValue "GIVEN_NAME" -< player lName <- getAttrValue "SURNAME" -< player returnA -< (leagName, diviName, teamName, fName, lName) -- What we really want is to capture the players in a list -- at this level; and if there are no players then the -- empty list will suffice. listA is used for this purpose. getPlayer1 = atTag "PLAYER" >>> proc p -> do fName <- getAttrValue "GIVEN_NAME" -< p lName <- getAttrValue "SURNAME" -< p returnA -< (fName, lName) getTeams3 = atTag "LEAGUE" >>> proc l -> do leagName <- getAttrValue "NAME" -< l divi <- atTag "DIVISION" -< l diviName <- getAttrValue "NAME" -< divi team <- atTag "TEAM" -< divi teamName <- getAttrValue "NAME" -< team players <- listA getPlayer1 -< team returnA -< (leagName, diviName, teamName, players) -- Try capturing some statistics about the players significant = not . all (`elem` " \n\r\t") -- Use our definition of "significant" strings to -- capture the value; or else nothing. defaultAttrStat attr = (getAttrValue attr >>> isA significant >>> arr Just) `orElse` (constA Nothing) getPlayer2 = atTag "PLAYER" >>> proc p -> do fName <- getAttrValue "GIVEN_NAME" -< p lName <- getAttrValue "SURNAME" -< p position <- getAttrValue "POSITION" -< p hits <- defaultAttrStat "HITS" -< p atBats <- defaultAttrStat "AT_BATS" -< p era <- defaultAttrStat "ERA" -< p returnA -< Player { firstName = fName, lastName = lName, position = position, hits = read `fmap` hits, atBats = read `fmap` atBats, era = read `fmap` era } getTeams4 = atTag "LEAGUE" >>> proc l -> do leagName <- getAttrValue "NAME" -< l divi <- atTag "DIVISION" -< l diviName <- getAttrValue "NAME" -< divi team <- atTag "TEAM" -< divi teamName <- getAttrValue "NAME" -< team city <- getAttrValue "CITY" -< team players <- listA getPlayer2 -< team returnA -< Team { league = leagName, division = diviName, teamName = teamName, city = city, players = players } -- Our final choices getPlayer = getPlayer2 getTeams = getTeams4 main = do teams <- runX (parseXML "simple2.xml" >>> getTeams) print teams