From c785a95f14f8bb3887cdc411ef3329533a2c819a Mon Sep 17 00:00:00 2001
From: Akshay <nerdy@peppe.rs>
Date: Fri, 9 Oct 2020 11:36:10 +0530
Subject: allow eval without entering repl

---
 bin/Main.hs | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/bin/Main.hs b/bin/Main.hs
index 2942566..591fc1e 100644
--- a/bin/Main.hs
+++ b/bin/Main.hs
@@ -1,15 +1,21 @@
 module Main where
 
+import           Control.Monad                 (liftM)
+import           Control.Monad.Except          (throwError)
+import           Error                         (LispError (..), LispResult (..),
+                                                unwrap)
 import           Evaluator                     (eval)
 import           Parser                        (Expr (..), parseLispValue)
 import           System.Console.Readline
+import           System.Environment            (getArgs)
 import           Text.ParserCombinators.Parsec
 
-readExpr :: String -> Expr
+readExpr :: String -> LispResult Expr
 readExpr inp =
     case parse parseLispValue "(unknown)" inp of
-      Left err  -> StringLiteral $ show err
-      Right val -> val
+      Left err  -> throwError $ Parse err
+      Right val -> return val
+
 
 repl :: IO ()
 repl = do
@@ -19,8 +25,15 @@ repl = do
       Just ",q" -> return ()
       Just line -> do
           addHistory line
-          print . eval . readExpr $ line
+          -- TODO: don't directly print Either values
+          print $ eval =<< readExpr line
           repl
 
 main :: IO ()
-main = repl
+main = do
+    args <- getArgs
+    if null args
+       then do
+           print ";;; Entering lisk repl ..."
+           repl
+       else print $ eval =<< readExpr (head args)
-- 
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