From 5097a20545bbeeafec191f97e9d0ae3d215ada90 Mon Sep 17 00:00:00 2001
From: Akshay <nerdy@peppe.rs>
Date: Fri, 9 Oct 2020 18:52:45 +0530
Subject: add binary boolean operators

---
 src/Error.hs     |  2 +-
 src/Operators.hs | 14 ++++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/Error.hs b/src/Error.hs
index 165cc5c..5ba48bf 100644
--- a/src/Error.hs
+++ b/src/Error.hs
@@ -20,7 +20,7 @@ unwordsList = unwords . map show
 instance Show LispError where
     show (Parse e)        = "Parser Error: " ++ show e
     show (BadForm s expr) = "Bad Form: " ++ s ++ ": " ++ show expr
-    show (ArgCount n es) = "Invalid arity, expected " ++ show n ++ ", got values: " ++ unwordsList es
+    show (ArgCount n es) = "Invalid arity, expected " ++ show n ++ ", got value(s): " ++ unwordsList es
     show (UnknownFunction fn) = "Cannot apply function: " ++ fn
     show (TypeMismatch msg got) = "Type mismatch, expected " ++ msg ++ ", got: " ++ show got
 
diff --git a/src/Operators.hs b/src/Operators.hs
index fc0608e..beb6364 100644
--- a/src/Operators.hs
+++ b/src/Operators.hs
@@ -13,10 +13,17 @@ primitives =
     , ("-", arithmetic (-))
     , ("*", arithmetic (*))
     , ("/", arithmetic (/))
+    , (">", comparator (>))
+    , ("<", comparator (<))
+    , (">=", comparator (>=))
+    , ("<=", comparator (<=))
+    , ("=", comparator (==))
+    , ("!=", comparator (/=))
     ]
 
 data LispNumber = I Integer
                 | F Double
+                deriving (Eq, Ord)
 
 instance Num LispNumber where
     -- TODO:
@@ -41,6 +48,13 @@ arithmetic op args
         as <- mapM unwrapNum args
         return . wrapNum $ foldl1 op as
 
+comparator :: (LispNumber -> LispNumber -> Bool) -> [Expr] -> LispResult Expr
+comparator op args
+    | length args < 2 = throwError $ ArgCount 2 args
+    | otherwise = do
+        as <- mapM unwrapNum args
+        return . BoolLiteral . all (== True) $ zipWith op as (tail as)
+
 unwrapNum :: Expr -> LispResult LispNumber
 unwrapNum (IntLiteral n)   =  return $ I n
 unwrapNum (FloatLiteral n) =  return $ F n
-- 
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