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+{- Main.hs -- main entry point
+Copyright (C) 2012  Benjamin Barenblat <benjamin@barenblat.name>
+
+This module is a part of ageOf.
+
+ageOf is free software: you can redistribute it and/or modify it under the
+terms of the GNU General Public License as published by the Free Software
+Foundation, either version 3 of the License, or (at your option) any later
+version.
+
+ageOf is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License along with
+ageOf.  If not, see <http://www.gnu.org/licenses/>. -}
+
+module Main where
+
+import Control.Monad (foldM)
+import System.Environment (getArgs, getProgName)
+import System.Exit (ExitCode(..), exitWith)
+import Text.Printf (printf)
+
+import RequestMethod (RequestMethod, getAge)
+import DBpedia (dbpedia)
+import SamplePlugin (samplePlugin)
+
+-- The plugins we're going to query, in order of preference.
+plugins :: [RequestMethod]
+plugins = [ samplePlugin
+          , dbpedia ]
+
+main :: IO ()
+main = getArgs >>= go >>= exitWith
+
+go :: [String] -> IO ExitCode
+go (name : []) = do
+  age <- getAgeWith plugins name
+  case age of
+    Nothing -> return $ ExitFailure 1
+    Just n -> print n >> return ExitSuccess
+go _ = usage >> return (ExitFailure 1)
+
+{- The workhorse function.  Given a list of 'RequestMethod's, 'getAgeWith'
+tries to look up 'name' in each one.  As soon as a match succeeds, it returns
+the age. -}
+getAgeWith :: [RequestMethod] -> String -> IO (Maybe Integer)
+getAgeWith methods name =
+  foldM maybeTryNextMethod Nothing methods
+  where maybeTryNextMethod :: Maybe Integer -> RequestMethod -> IO (Maybe Integer)
+        maybeTryNextMethod v@(Just _) _ = return v
+        maybeTryNextMethod Nothing method = getAge method name
+
+usage :: IO ()
+usage = do
+  programName <- getProgName
+  printf "usage: %s <name>\n" programName