REPL import warning; version info in CLI

Adds the ability to toggle result decoding in REPL. Adds several more
useful functions to the base library.

src/Main.hs

@@ -8,7 +8,9 @@ import Research
 
 import Control.Monad          (foldM)
 import Control.Monad.IO.Class (liftIO)
+import Data.Version           (showVersion)
 import Text.Megaparsec        (runParser)
+import Paths_tricu            (version)
 import System.Console.CmdArgs
 
 import qualified Data.Map as Map
@@ -52,10 +54,12 @@ decodeMode = TDecode
 
 main :: IO ()
 main = do
+  let versionStr = "tricu Evaluator and REPL " ++ showVersion version
   args <- cmdArgs $ modes [replMode, evaluateMode, decodeMode]
     &= help "tricu: Exploring Tree Calculus"
     &= program "tricu"
-    &= summary "tricu Evaluator and REPL"
+    &= summary versionStr
+    &= versionArg [explicit, name "version", summary versionStr]
   case args of
     Repl -> do
       putStrLn "Welcome to the tricu REPL"