diff --git a/clib/json11.cpp b/clib/json11.cpp
index 0ed523e..4ef6e8b 100644
--- a/clib/json11.cpp
+++ b/clib/json11.cpp
@@ -125,8 +125,7 @@ namespace json11 {
 ////////////////////////
 
     static MlValue ivalualize(NullStruct) {
-	    MlValue null;
-	    return null;
+	    return  MlValue::nil();
     }
 
     static MlValue ivalualize(double value) {
diff --git a/debug.lsp b/debug.lsp
index 8790da6..5a05629 100644
--- a/debug.lsp
+++ b/debug.lsp
@@ -1,8 +1,3 @@
-;; (print
-;; "ahoj"
-;; ; this comment is problem
-;; )
-;; (print "lisp")
-
-; (define l '(1 2 2 2 3 4 5 4 4 1 2 2 2 3 4 5 4 4 61 2 2 2 3 4 5 4 4 66)
-
+(define json_list (parse-json "{\"k1\":\"v1\", \"k2\":42, \"k3\":[\"a\",123,true,false,null]}"))
+(print json_list)
+(for x json_list (print x))
\ No newline at end of file
diff --git a/ml.cpp b/ml.cpp
index 7216b9c..cfb1e73 100644
--- a/ml.cpp
+++ b/ml.cpp
@@ -22,6 +22,7 @@
 #define TOO_FEW_ARGS "too few arguments to function"
 #define TOO_MANY_ARGS "too many arguments to function"
 #define INVALID_ARGUMENT "invalid argument"
+#define INVALID_ARGUMENT_NIL "invalid nil argument"
 #define MISMATCHED_TYPES "mismatched types"
 #define CALL_NON_FUNCTION "called non-function"
 #define UNKNOWN_ERROR "unknown exception"
@@ -38,7 +39,6 @@
 #define STRING_TYPE "string"
 #define INT_TYPE "int"
 #define FLOAT_TYPE "float"
-#define UNIT_TYPE "unit"
 #define NIL_TYPE "nil"
 #define FUNCTION_TYPE "function"
 #define ATOM_TYPE "atom"
@@ -57,7 +57,7 @@ bool is_symbol(char ch) {
 }
 
 
-MlValue::MlValue() : type(UNIT) {}
+MlValue::MlValue() : type(NIL) {}
 
 MlValue::MlValue(int i) : type(INT) { stack_data.i = i; }
 
@@ -335,10 +335,8 @@ bool MlValue::operator<(const MlValue &other) const {
 
 // This function adds two lisp values, and returns the lisp value result.
 MlValue MlValue::operator+(const MlValue &other) const {
-	// If the other value's type is the unit type,
-	// don't even bother continuing.
-	// Unit types consume all arithmetic operations.
-	if (other.type == UNIT) return other;
+	if (other.type == NIL)
+		throw MlError(*this, MlEnvironment(), INVALID_ARGUMENT_NIL);
 
 	// Other type must be a float or an int
 	if ((is_number() || other.is_number()) &&
@@ -374,8 +372,6 @@ MlValue MlValue::operator+(const MlValue &other) const {
 				return result;
 
 			} else throw MlError(*this, MlEnvironment(), INVALID_BIN_OP);
-		case UNIT:
-			return *this;
 		default:
 			throw MlError(*this, MlEnvironment(), INVALID_BIN_OP);
 	}
@@ -383,10 +379,8 @@ MlValue MlValue::operator+(const MlValue &other) const {
 
 // This function subtracts two lisp values, and returns the lisp value result.
 MlValue MlValue::operator-(const MlValue &other) const {
-	// If the other value's type is the unit type,
-	// don't even bother continuing.
-	// Unit types consume all arithmetic operations.
-	if (other.type == UNIT) return other;
+	if (other.type == NIL)
+		throw MlError(*this, MlEnvironment(), INVALID_ARGUMENT_NIL);
 
 	// Other type must be a float or an int
 	if (other.type != FLOAT && other.type != INT)
@@ -404,9 +398,6 @@ MlValue MlValue::operator-(const MlValue &other) const {
 				return MlValue(cast_to_float().stack_data.f - other.stack_data.f);
 				// Otherwise, do integer subtraction.
 			else return MlValue(stack_data.i - other.stack_data.i);
-		case UNIT:
-			// Unit types consume all arithmetic operations.
-			return *this;
 		default:
 			// This operation was done on an unsupported type
 			throw MlError(*this, MlEnvironment(), INVALID_BIN_OP);
@@ -415,10 +406,8 @@ MlValue MlValue::operator-(const MlValue &other) const {
 
 // This function multiplies two lisp values, and returns the lisp value result.
 MlValue MlValue::operator*(const MlValue &other) const {
-	// If the other value's type is the unit type,
-	// don't even bother continuing.
-	// Unit types consume all arithmetic operations.
-	if (other.type == UNIT) return other;
+	if (other.type == NIL)
+		throw MlError(*this, MlEnvironment(), INVALID_ARGUMENT_NIL);
 
 	// Other type must be a float or an int
 	if (other.type != FLOAT && other.type != INT)
@@ -434,9 +423,6 @@ MlValue MlValue::operator*(const MlValue &other) const {
 				return MlValue(cast_to_float().stack_data.f * other.stack_data.f);
 				// Otherwise, do integer multiplication.
 			else return MlValue(stack_data.i * other.stack_data.i);
-		case UNIT:
-			// Unit types consume all arithmetic operations.
-			return *this;
 		default:
 			// This operation was done on an unsupported type
 			throw MlError(*this, MlEnvironment(), INVALID_BIN_OP);
@@ -445,10 +431,8 @@ MlValue MlValue::operator*(const MlValue &other) const {
 
 // This function divides two lisp values, and returns the lisp value result.
 MlValue MlValue::operator/(const MlValue &other) const {
-	// If the other value's type is the unit type,
-	// don't even bother continuing.
-	// Unit types consume all arithmetic operations.
-	if (other.type == UNIT) return other;
+	if (other.type == NIL)
+		throw MlError(*this, MlEnvironment(), INVALID_ARGUMENT_NIL);
 
 	// Other type must be a float or an int
 	if (other.type != FLOAT && other.type != INT)
@@ -464,9 +448,6 @@ MlValue MlValue::operator/(const MlValue &other) const {
 				return MlValue(cast_to_float().stack_data.f / other.stack_data.f);
 				// Otherwise, do integer multiplication.
 			else return MlValue(stack_data.i / other.stack_data.i);
-		case UNIT:
-			// Unit types consume all arithmetic operations.
-			return *this;
 		default:
 			// This operation was done on an unsupported type
 			throw MlError(*this, MlEnvironment(), INVALID_BIN_OP);
@@ -475,10 +456,8 @@ MlValue MlValue::operator/(const MlValue &other) const {
 
 // This function finds the remainder of two lisp values, and returns the lisp value result.
 MlValue MlValue::operator%(const MlValue &other) const {
-	// If the other value's type is the unit type,
-	// don't even bother continuing.
-	// Unit types consume all arithmetic operations.
-	if (other.type == UNIT) return other;
+	if (other.type == NIL)
+		throw MlError(*this, MlEnvironment(), INVALID_ARGUMENT_NIL);
 
 	// Other type must be a float or an int
 	if (other.type != FLOAT && other.type != INT)
@@ -492,9 +471,6 @@ MlValue MlValue::operator%(const MlValue &other) const {
 			if (other.type == FLOAT)
 				return MlValue(fmod(cast_to_float().stack_data.f, other.stack_data.f));
 			else return MlValue(stack_data.i % other.stack_data.i);
-		case UNIT:
-			// Unit types consume all arithmetic operations.
-			return *this;
 		default:
 			// This operation was done on an unsupported type
 			throw MlError(*this, MlEnvironment(), INVALID_BIN_OP);
@@ -522,8 +498,6 @@ std::string MlValue::get_type_name() {
 			// lambda and builtin types, we group them together.
 			// This is because they are both callable.
 			return FUNCTION_TYPE;
-		case UNIT:
-			return UNIT_TYPE;
 		case NIL:
 			return NIL_TYPE;
 		default:
@@ -561,8 +535,6 @@ std::string MlValue::display() const {
 			return "(" + result + ")";
 		case BUILTIN:
 			return "<" + str + " at " + to_string(long(stack_data.b)) + ">";
-		case UNIT:
-			return "@";
 		case NIL:
 			return "nil";
 		default:
@@ -604,8 +576,6 @@ std::string MlValue::debug() const {
 			return "(" + result + ")";
 		case BUILTIN:
 			return "<" + str + " at " + to_string(long(stack_data.b)) + ">";
-		case UNIT:
-			return "@";
 		case NIL:
 			return "nil";
 		default:
diff --git a/ml.h b/ml.h
index 39b1973..fa9c685 100644
--- a/ml.h
+++ b/ml.h
@@ -77,7 +77,7 @@ typedef MlValue (*Builtin)(std::vector<MlValue>, MlEnvironment &);
 class MlValue {
 public:
 
-    // Constructs a unit value
+    // Constructs a nil value
     MlValue();
 
     // Constructs an integer
@@ -200,7 +200,6 @@ private:
 	STRING,
 	LAMBDA,
 	BUILTIN,
-	UNIT,
 	NIL
     } type;