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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
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