Add --version flag. Fixes #8

bench.cabal

@@ -1,5 +1,5 @@
 name:                bench
-version:             1.0.1
+version:             1.0.2
 synopsis:            Command-line benchmark tool
 description:         Think of this as a more powerful alternative to the @time@
                      command.  Use this command-line tool to benchmark a command
@@ -25,9 +25,10 @@ executable bench
   hs-source-dirs:      src
   main-is:             Main.hs
   default-language:    Haskell2010
-  build-depends:       base      >= 4.5     && < 5
-                     , criterion >= 1.1.1.0 && < 1.2
-                     , text                    < 1.3
-                     , silently  >= 1.1.1   && < 1.3
-                     , turtle    >= 1.2.5   && < 1.3
+  build-depends:       base                 >= 4.5     && < 5
+                     , criterion            >= 1.1.1.0 && < 1.2
+                     , optparse-applicative >= 0.2.0   && < 0.14
+                     , silently             >= 1.1.1   && < 1.3
+                     , text                               < 1.3
+                     , turtle               >= 1.2.5   && < 1.3
   ghc-options:         -Wall -O2 -threaded

src/Main.hs

@@ -4,47 +4,59 @@
 module Main where
 
 import Control.Applicative
+import Data.Monoid ((<>))
 import Data.Text (Text)
-import Turtle (Parser)
+import Turtle (Parser, s, (%))
 
 import qualified Criterion
 import qualified Criterion.Main         as Criterion
 import qualified Criterion.Main.Options as Criterion
 import qualified Data.Text              as Text
+import qualified Options.Applicative
 import qualified System.IO              as IO
 import qualified System.IO.Silently     as Silently
 import qualified Turtle
 
-data Options = Options
-    { cmd        :: [Text]
-    , mode       :: Criterion.Mode
-    } deriving (Show)
+version :: Text
+version = "1.0.2"
+
+data Options = Options [Text] Criterion.Mode | Version deriving (Show)
 
 parser :: Parser Options
 parser =
-        Options
-    <$> some (Turtle.argText "command(s)" "The command line(s) to benchmark")
-    <*> Criterion.parseWith Criterion.defaultConfig
+            Version
+        <$  Options.Applicative.flag'
+                ()
+                (   Options.Applicative.short 'v'
+                <>  Options.Applicative.long "version"
+                <>  Options.Applicative.help "Version number"
+                )
+    <|>     Options
+        <$> some
+                (Turtle.argText "command(s)" "The command line(s) to benchmark")
+        <*> Criterion.parseWith Criterion.defaultConfig
 
 main :: IO ()
 main = do
-    o <- Turtle.options "Command-line tool to benchmark other programs" parser
-    case (cmd o) of
-      [command] -> benchCommand command o
-      commands  -> benchCommands commands o
-
-benchCommands :: [Text] -> Options -> IO ()
-benchCommands commands opts@Options{..} = do
-    let benches = map (\command -> buildBench command opts) commands
+    x <- Turtle.options "Command-line tool to benchmark other programs" parser
+    case x of
+        Options [command] mode -> benchCommand  command mode
+        Options  commands mode -> benchCommands commands mode
+        Version -> do
+            Turtle.printf ("bench version "%s%"\n") version
+
+benchCommands :: [Text] -> Criterion.Mode -> IO ()
+benchCommands commands mode = do
+    let benches = map buildBench commands
     Criterion.runMode mode [Criterion.bgroup "bench" benches]
 
-benchCommand :: Text -> Options -> IO ()
-benchCommand command opts@Options{..} = do
-    let bench = buildBench command opts
+benchCommand :: Text -> Criterion.Mode -> IO ()
+benchCommand command mode = do
+    let bench = buildBench command
     Criterion.runMode mode [ bench ]
 
-buildBench :: Text -> Options -> Criterion.Benchmark
-buildBench command Options{..} = do
+buildBench :: Text -> Criterion.Benchmark
+buildBench command = do
     let io        = Turtle.shells command empty
     let benchmark = Criterion.nfIO (Silently.hSilence [IO.stdout, IO.stderr] io)
     let bench     = Criterion.bench (Text.unpack command) benchmark