Make minor improvements to parser

app/Main.hs

@@ -2,6 +2,7 @@ module Main (main) where
 
 import Control.Monad.Combinators.Expr
 import Data.Void (Void)
+import System.Environment
 import Text.Megaparsec
 import Text.Megaparsec.Char as C
 import Text.Megaparsec.Char.Lexer as L
@@ -46,6 +47,7 @@ expr = makeExprParser term table
 parseExpr :: String -> Either (ParseErrorBundle String Void) Expr
 parseExpr = parse (C.space *> expr <* eof) ""
 
-main :: IO ()
+-- main :: IO ()
 main = do
-  print $ parseExpr "2+3* 4"
+  input <- fmap head getArgs
+  parseTest expr input