1 files changed, 42 insertions, 0 deletions
diff --git a/evaluator/evaluator.go b/evaluator/evaluator.go
index 8d1b26d..0cc003f 100644
--- a/evaluator/evaluator.go
+++ b/evaluator/evaluator.go
@@ -5,6 +5,12 @@ import (
 	"mana/object"
 )
 
+var (
+	NULL  = &object.Null{}
+	TRUE = &object.Boolean{Value: true}
+	FALSE = &object.Boolean{Value: false}
+)
+
 // Eval evaluates the given ast.Node and returns an object.Object.
 func Eval(node ast.Node) object.Object {
 	switch node := node.(type) {
@@ -18,6 +24,13 @@ func Eval(node ast.Node) object.Object {
 	// Expressions
 	case *ast.IntegerLiteral:
 		return &object.Integer{Value: node.Value}
+
+	case *ast.Boolean:
+		return nativeBoolToBooleanObject(node.Value)
+
+	case *ast.PrefixExpression:
+		right := Eval(node.Right)
+		return evalPrefixExpression(node.Operator, right)
 	}
 
 	return nil
@@ -32,3 +45,32 @@ func evalStatements(stmts []ast.Statement) object.Object {
 
 	return result
 }
+
+func nativeBoolToBooleanObject(input bool) *object.Boolean {
+	if input {
+		return TRUE
+	}
+	return FALSE
+}
+
+func evalPrefixExpression(operator string, right object.Object) object.Object {
+	switch operator {
+	case "!":
+		return evalBangOperatorExpression(right)
+	default:
+		return NULL
+	}
+}
+
+func evalBangOperatorExpression(right object.Object) object.Object {
+	switch right {
+	case TRUE:
+		return FALSE
+	case FALSE:
+		return TRUE
+	case NULL:
+		return TRUE
+	default:
+		return FALSE
+	}
+}