added string concatenation

2 files changed, 31 insertions, 0 deletions

diff --git a/evaluator/evaluator.go b/evaluator/evaluator.go
index 9129a98..0eadd92 100644
--- a/evaluator/evaluator.go
+++ b/evaluator/evaluator.go
@@ -198,6 +198,8 @@ func evalInfixExpression(operator string, left, right object.Object) object.Obje
 	switch {
 	case left.Type() == object.INTEGER_OBJ && right.Type() == object.INTEGER_OBJ:
 		return evalIntegerInfixExpression(operator, left, right)
+	case left.Type() == object.STRING_OBJ && right.Type() == object.STRING_OBJ:
+		return evalStringInfixExpression(operator, left, right)
 	case operator == "==":
 		return nativeBoolToBooleanObject(left == right)
 	case operator == "!=":
@@ -260,6 +262,17 @@ func evalIntegerInfixExpression(operator string, left, right object.Object) obje
 	}
 }
 
+func evalStringInfixExpression(operator string, left, right object.Object) object.Object {
+	if operator != "+" {
+		return newError("unknown operator: %s %s %s", left.Type(), operator, right.Type())
+	}
+
+	leftVal := left.(*object.String).Value
+	rightVal := right.(*object.String).Value
+
+	return &object.String{Value: leftVal + rightVal}
+}
+
 func evalIfExpression(ie *ast.IfExpression, env *object.Environment) object.Object {
 	condition := Eval(ie.Condition, env)
 	if isError(condition) {
diff --git a/evaluator/evaluator_test.go b/evaluator/evaluator_test.go
index cf9e320..9738d9e 100644
--- a/evaluator/evaluator_test.go
+++ b/evaluator/evaluator_test.go
@@ -181,6 +181,10 @@ func TestErrorhandling(t *testing.T) {
 			"foobar",
 			"identifier not found: foobar",
 		},
+		{
+			`"Hello" - "World"`,
+			"unknown operator: STRING - STRING",
+		},
 	}
 
 	for _, tt := range tests {
@@ -327,3 +331,17 @@ func TestStringLiteral(t *testing.T) {
 		t.Errorf("String has wrong value. got=%q", str.Value)
 	}
 }
+
+func TestStringConcatenation(t *testing.T) {
+	input := `"Hello" + " " + "World!"`
+
+	evaluated := testEval(input)
+	str, ok := evaluated.(*object.String)
+	if !ok {
+		t.Fatalf("object is not String. got=%T (%+v)", evaluated, evaluated)
+	}
+
+	if str.Value != "Hello World!" {
+		t.Errorf("String has wrong value. got=%q", str.Value)
+	}
+}