From a170eb4450ba6c130532efd25edbf7ed628510d6 Mon Sep 17 00:00:00 2001
From: tijani <tijani@tijanilawal.com>
Date: Mon, 8 Aug 2022 11:01:32 +0000
Subject: [PATCH] Infix evaluation operation now supported.

git-svn-id: https://svn.tlawal.org/svn/monkey@47 f6afcba9-9ef1-4bdd-9b72-7484f5705bac
---
 evaluator/evaluator.go      | 10 ++++++++++
 evaluator/evaluator_test.go |  3 +++
 2 files changed, 13 insertions(+)

diff --git a/evaluator/evaluator.go b/evaluator/evaluator.go
index 632ad2b..241c241 100644
--- a/evaluator/evaluator.go
+++ b/evaluator/evaluator.go
@@ -56,6 +56,8 @@ func eval_prefix_expression(operator string, right object.Object) object.Object
 	switch operator {
 	case "!":
 		return eval_bang_operator_expression(right)
+	case "-":
+		return eval_minus_prefix_operator_expression(right)
 
 	default:
 		return NULL
@@ -77,3 +79,11 @@ func eval_bang_operator_expression(right object.Object) object.Object {
 		return FALSE
 	}
 }
+
+func eval_minus_prefix_operator_expression(right object.Object) object.Object {
+	if right.Type() != object.INTEGER_OBJECT{
+		return NULL
+	}
+	value := right.(*object.Integer).Value
+	return &object.Integer{Value: -value}
+}
diff --git a/evaluator/evaluator_test.go b/evaluator/evaluator_test.go
index cb6e505..63055ff 100644
--- a/evaluator/evaluator_test.go
+++ b/evaluator/evaluator_test.go
@@ -14,6 +14,9 @@ func TestEvalIntegerExpression(l_test *testing.T) {
 	}{
 		{"5", 5},
 		{"10", 10},
+		{"-10", -10},
+		{"-5", -5},
+
 	}
 
 	for _, tt := range tests {