Adding mod

src/Expressions.hs

@@ -14,6 +14,10 @@ data Atom =
     AFalse |
     ANothing
 
+_fromBool :: Bool -> Atom
+_fromBool True  = ATrue
+_fromBool False = AFalse
+
 newtype SExpr = SExpr [Statement]
 
 instance Show Atom where

src/LispEnv.hs

@@ -41,11 +41,6 @@ evalCdr [Expr expr] env = do
 evalCdr [Atom bad] _ = Left $ "**Error: " ++ show bad ++ " is not a pair.**"
 evalCdr _ _ = Left "**Error: incorect argument count in cdr**"
 
-
-_fromBool :: Bool -> Atom
-_fromBool True  = ATrue
-_fromBool False = AFalse
-
 evalEq :: [Statement] -> LispEnv -> Either String (Atom, LispEnv)
 evalEq [Atom (AInt f), Atom (AInt s)] env = Right (_fromBool (f == s), env)
 evalEq [Atom (ASymbol f), Atom (ASymbol s)] env = Right (_fromBool (f == s), env)

src/Maths.hs

@@ -8,7 +8,8 @@ mathEnv = [
         ("-", ABuiltin "-" evalMinus),
         ("*", ABuiltin "*" evalMult),
         ("div", ABuiltin "div" evalDiv),
-        ("mod", ABuiltin "mod" evalMod)
+        ("mod", ABuiltin "mod" evalMod),
+        ("<", ABuiltin "<" evalLessThan)
     ]
 
 evalPlus :: [Statement] -> LispEnv -> Either String (Atom, LispEnv)
@@ -72,4 +73,17 @@ evalMod [Expr expr, other] env = do
 evalMod [other, Expr expr] env = do
     (res, nEnv) <- evalS expr env
     evalMod [other, Atom res] nEnv
-evalMod _ _ = Left "**Error: Invalid arguments in mod.**"
+evalMod _ _ = Left "**Error: Invalid arguments in mod.**"
+
+evalLessThan :: [Statement] -> LispEnv -> Either String (Atom, LispEnv)
+evalLessThan [Atom (AInt f), Atom (AInt s)] env = Right (_fromBool (f < s), env)
+evalLessThan [Atom (AFloat f), Atom (AFloat s)] env = Right (_fromBool (f < s), env)
+evalLessThan [Atom (AFloat f), Atom (AInt s)] env = Right (_fromBool (f < fromIntegral s), env)
+evalLessThan [Atom (AInt f), Atom (AFloat s)] env = Right (_fromBool (fromIntegral f < s), env)
+evalLessThan [Expr expr, other] env = do
+    (res, nEnv) <- evalS expr env
+    evalLessThan [Atom res, other] nEnv
+evalLessThan [other, Expr expr] env = do
+    (res, nEnv) <- evalS expr env
+    evalLessThan [other, Atom res] nEnv
+evalLessThan _ _ = Left "**Error: Invalid arguments in <.**"